It hasn't been updated in quite awhile, and I have heard some Lemmy features are still broken - I think some types of inline images and markdown mainly, and some upcoming api changes may break it completely in the nearish future.

Here is a comment I made in a relevant thread, where they discuss sync (here: https://lemmy.world/comment/14130358)

As someone who used sync on reddit for many years, I switched to Summit a few weeks ago and it's great. This post comparing a lot of lemmy apps made me finally take the plunge: https://lemmy.world/post/18159531

TLDR: A lot of formatting is messed up on sync.

I was in the same boat; I've been using sync for years. Recently, I've definitely noticed issues with certain instances and comment sections. Search was also completely broken. According to what I've read, it appears to be a version mismatch issue. Since sync hasn't been updated in a year, I've cancelled my subscription and moved over to Summit.

Just started using Thunder and it is a pretty easy transition from Sync.