What you said makes sence, and yes I have the photo syncing turned on.
But, let me try the following (just reseting to factory the phone with AOKP) … as soon as I get the phone empty, I will install f-droid, then YALP (no GAPPS) and then the seafile client from the G-Play Store (the one on f-droid has sync issues). With no account added yet, will check if the app is on the internal storage or the SD. If its in the SD will move to internal and then reset the phone, add the new account and reset it again.
Will keep you posted on any findings.