Play store error #963
When using the methods reported by @Izzy, none of them solved the issue on my Galaxy On7, rooted to work with Android Pie (9), LineageOS 16 flavour -- using an SD Card as adopted storage.

Here is what I did:


After enabling Developer Options, I checked the option "Force Allow apps on external" 
Cleared the play store data;
Rebooted the device


Now all apps on playstore, which I had forcibly moved to the sd card with Titanium Backup, are able to be updated with no issues.

Hope this helps