How did Mo Jun Jie's hearing aid end up at the crime scene? I remember Chen Yun Ru gave it back to him. She also clearly lied to the police about what actually happened. Was it ever explained?

I don't think it was ever explained. The plot revolving around the murders is always confusing, in fact, I still don't know why Mo Junjie became the suspect in the future where Yunru died.

Came here looking for that answer too. I guess they just forgot to adress that. Also as soon as she jumps to her death the cops are nearby and ready to arrest Mo Jun Jie. No evidence to convict him. I liked the drama but there's just a few things they could have fleshed out to make it a bit better.  

About hearing aid, the original scriptwriter replies this as NO.11 of "More info" in the following link:

https://mydramalist.com/discussions/some-day-or-one-day/46677-translated-very-long-has-spoilers-interview-and-other-infos

The Korean remake provides the explanation exactly same as I thought, but it is so easy to guess.
So far, I don't believe the original scriptwriter's answer. I guess he must make this part too complicated to make sense. You know that guy really tried to make the script not easy to guess.

Thanks for the replies! I personally think the reason Mo Jun Jie was arrested was because he was there but didn't say anything to the police. Maybe the glass shard had his fingerprints too. Also in that time Chen Yun Ru's attacker was never arrested and Mo Jun Jie was a previous suspect in it.

 David Sun:

About hearing aid, the original scriptwriter replies this as NO.11 of "More info" in the following link:

https://mydramalist.com/discussions/some-day-or-one-day/46677-translated-very-long-has-spoilers-interview-and-other-infos

The Korean remake provides the explanation exactly same as I thought, but it is so easy to guess.
So far, I don't believe the original scriptwriter's answer. I guess he must make this part too complicated to make sense. You know that guy really tried to make the script not easy to guess.

You dpon't believe the scriptwiter's answer that it got cut because of time constraints? THAT'S bizarre. It's the simplest and most likely explanation. TW Dramas are always longer than they should be anyway, and every Drama everywhere has scenes cut because of time constraints. Why would you doubt the person who actually wrote the script? They have no reason or motive to lie, which is what you're saying they did.