Douban post from a member of the production team about the difficulties faced to get this drama aired:
"In fact, it was not easy for this drama to be aired smoothly. The trial was full of twists and turns. First, it was stuck in November because of the epidemic. After it was released, it was rejected twice because of the content and theme. In fact, it was mid-December. At that time, our project team was fully prepared for the possible postponement. It is estimated that the luck of the leading actors and our friends is very good, and the certificate was issued on 12/20. Last year, the review was particularly strict, especially for the key projects. It is ridiculous that an A-level project was changed to a key project because of the traffic(meaning Dylan's popularity due to LBFAD). The 16th (not sure what the person meant by this) is a project that my friend contacted, and it was returned and deleted after finalized. I don't know what those in charge were thinking. In fact, there is no second trial for Forbidden Love. Firstly, I am afraid that there will be changes in ancient drama's policy this year. I can say that Forbidden Love's intimate scenes are already many this year because there is no second trial."

From above statement, the following reasons for strict censorship were:

1. Content and theme

2. Dylan's popularity caused an A-level (low-budget) project to be changed to a key project incurring stricter review

Thanks for the info. I now understand.

You're welcome :)

In other threads, there were conjectures of another reason for the cuts - sabotage.

I just saw a video by a YouTuber called "aini", titled China has soft power deficiency although she doesn't mention FTY (it was before it was released) but she basically said that the dramas, novels, or any speech, despite having immense potential, is stopped by the government when it "doesn't fit the government rules". 

That's true. Last year, BL dramas were stopped from airing. Around 3rd quarter last year, a film director reported that new rules to regulate the Chinese entertainment industry are going to be implemented. He deleted his post but not before some netizens took note of it. Among the new rules he mentioned are:

1. Romance dramas packaged as military dramas will not pass review. military dramas cannot use "little fresh meat"
2. Costume dramas' costumes and make-up need to be serious and fit the era
3. Actors with obvious or abnormal plastic surgery are not allowed, especially not for military or public security themed dramas. no "sissy aesthetics" and no excessive make-up
4. 60% of all dramas should be realistic, not less than 20% should be about the historical revolution
5. Variety show singers and dancers cannot lead dramas. traffic stars canot lead dramas with important issues
6. Realistic dramas are strongly encouraged
7. CP or couple marketing is not allowed 

I agree with the realistic ones but the rest of them are just too much! Like yeah the casting should totally depend on the producers and casting directors, not the government! They're basically ruining it for China ironically.

The post was deleted, so I have a feeling the list was just a draft, not an official one. I wonder if official rules are publicized in China.

Cp marketing is getting banned??? Big companies won't like it i mean how will they earn money without co marketing...

And why can't reality tv shows singers and dancers lead dramas?? I mean what's srong with them leading drama until and unless they do a good job...for example wang yibo whose both a singer and a dancer that means he can't lead any drama in future???

Well i feel it's maybe false and if it's true then it's too unrealistic...

I think these are restrictions but whether they are enforced or not remains to be seen. 

Regarding CP marketing, I also don't know why it is getting banned. But I think CP worship can be detrimental to performers' career growth. In fact, I think it reared its ugly head in this drama. It seems that fans of Dylan's former CP's have been attacking Yukee and this drama.

Regarding TV shows and singers not leading dramas, I think this might be a way to control the influence of celebrities and avoid monopoly of popularity, and perhaps to give others a chance to shine.

Ik what you mean and tbh i really hate it when I see all the hate that Chen yuqi is getting from yu shuxin-wang hedi cp fans but i feel that a large part of c drama industry thrive on cp marketing...( For example Zhang zhehan and gong Juns cp marketing scandal that u might be aware of ) from there we can see how important cp marketing is for a company...

Also as u said the monopoly thing we all know those with talent only survive i the showbiz.. so i don't think it wud affect anything and honestly if a singer/ dancer can act then what's wrong with them being popular...

Considering the "cancel culture" in China, I've long felt the govt does not care much for the entertainment industry except as possible propaganda tool. And super popular and rich celebrities like Jack Ma, formerly of Alibaba (the Amazon of China), seem to be eyed with wariness, to be pulled down at the first sign of being critical of authorities.

So perhaps keeping music and dramas/film separate is an attempt to limit the influence of celebrities.

Yea i k what you mean by that... Till date people are not sure where the super powerful jack ma is living these days... If he's alive or dead... His only clime he was against the government...

Chinese government is too powerful and people don't dare to go against them ..

I have a friend who grew up in mainland China and is now living in HK she told me that they are taught in schools to be politically tolerant and passive in political matters... They are taught to just support the government and never go against it....

And as for influence of idols and celebrities i don't think it is easy to limit it... If they will limit Chinese celebrities then Korean idols and celebrities will gain more followers which is not something the Chinese government wud like .....  U know how much the Chinese government loves Korea...

So it wud be like shooting yourself in foot...

Let's see... what happens 

 magnolia cream:

That's true. Last year, BL dramas were stopped from airing. Around 3rd quarter last year, a film director reported that new rules to regulate the Chinese entertainment industry are going to be implemented. He deleted his post but not before some netizens took note of it. Among the new rules he mentioned are:

1. Romance dramas packaged as military dramas will not pass review. military dramas cannot use "little fresh meat"
2. Costume dramas' costumes and make-up need to be serious and fit the era
3. Actors with obvious or abnormal plastic surgery are not allowed, especially not for military or public security themed dramas. no "sissy aesthetics" and no excessive make-up
4. 60% of all dramas should be realistic, not less than 20% should be about the historical revolution
5. Variety show singers and dancers cannot lead dramas. traffic stars canot lead dramas with important issues
6. Realistic dramas are strongly encouraged
7. CP or couple marketing is not allowed 

"Variety show singers and dancer cannot lead dramas." What load BS is that. 

I agree, this list is questionable, which is why I think it's a draft at best, probably the reason the post was deleted. Regarding bullet point #5 "Variety show singers and dancer cannot lead dramas", I've been wondering whether that figured in Zhang Zhehan's cancellation, i.e., singer-actors are being forced to choose which field to concentrate on. As to why, possibly to limit a celebrity's influence since China seems to be wary of celebrities having too much influence. Case in point - Jack Ma. There is an earlier discussion above about this.