Syncing mkv to iOS, hit or miss?

Wanted to ask a question about syncing MKV files to iOS devices specifically an iPad.
I currently have the entire Fringe TV series in mkv format and I have been trying to sync seasons To my iPad. If I try to sync the entire season about half of the episodes will come back with an error about unable to transcode, I don’t recall the error exactly but I can reproduce. When the iPad shows those failures, my only option is to delete the entire season and then go back and try and sync each episode individually. Some of the same episodes that would fail when doing the entire series also fail individually but if I try repeatedly to have them sync they eventually go through. Possibly irrelevant, but it seems if a episode fails when requested from the iPad Plex app, it will succeed if I schedule the sync from a browser and vice versa for a sync requested from a browser.
I have seen some posts about the syncing ability to iOS devices sometimes been problematic, but I wasn’t sure if that had been fixed in the last couple months. My server is up to date with the current Plex build.
So my question to those reading this post is how common are syncing issues in either MKV or other formats when destined to an iPad or iOS device.

I’m using the public 4.22 and it’s flawless to both an ipad 4 and ipad pro