Library not syncing on iPad or iPhone

The iPad and iPhone correspond and each have only managed to load 28 out of over 300 entries over the last week, trying multiple times a day. Often the app crashes, it doesn’t seem to run sync in the background while I do other things and it’s not making any progress. Endnote on the PC is the latest version, iPad is running 14.7.1. 

I can’t even load the IPad app for long enough to check the settings - it freezes as I open up any page while syncing, and it never finishes syncing. 

Is there something fundamental I am missing here?