I don’t have it installed right now, as I’ve been trying out a FOSS reader for a while now on my new phone, but there is a troubleshooting section about syncing on their site, and also they recommend this guide made by a user discussing sync troubleshooting.

It’s not a feature I’ve used, so maybe those guides have something you haven’t tried. Since you replied to me though, I feel partially responsible for making sure you get helped now. 😅