problems with syncing on fireos / plex app

Hi,
Trying to sync a few shows to my Amazon Fire HD 8. I have the google playstore on the device and added plex via that. I will setup the sync to go to the external SD card (128 GB) and start syncing some shows. Invariably when I check back later, it has flipped back to internal storage and run my device out of space.
I think there is a bug here.
Are there any additional details to include? I don’t see a spot for log files in the settings of the app.
Device Model: Fire HD 8 (6th Generation)
OS version: Fire OS 5.3.2.1
Plex player version:5.6.505(25ece77b)