I use an old phone for reading these days it has no mobile connection so only syncs positions when I am connected to wifi. I think the OP would be doing the same an IPad with no internet connection when on the go. On android I use coolreader for sync. Another app that supports is koreader as coolreader seems to have been abandoned.
https://github.com/buggins/coolreader
https://github.com/koreader/koreader
I hope the devs of koreader someday add support for Calibre progress sync directly so that there is no need to run a 2nd app for syncing progress instead it is done with Calibre