I’d say that, from the bug reports I can see around, the XA2 is the most functional SFOS official phone.
Indeed, what you describe unusual and should not be.
I also have an XA2. Experience is smooth and excellent apart some small bugs one can live with.
(I had like many (6?) XA2, Dual and Single SIM, for me and friends/family.)
In your situation, I’d reflash Android on Windows and then reflash SFOS.
I’m using these binaries: SW_binaries_for_Xperia_Android_8.1.6.4_r1_v16_nile.zip (not v17)
About the GPS, it is a common issue on the XA2. It can be fixed. See
About backup/restore, the SFOS backup is (was?) not working correctly.
I’d rather use rsync from a PC through ssh. See here and here, or else with the forum serach engine and the keywords “ssh“, “rsync”…