Have you tried using heliboard or floris keyboard? I had some minor issues with AOSP keyboard on lineageOS and I tried these two, both worked flawlessly and I would recommend them over the AOSP one. I disabled the AOSP keyboard.
KInd of unrelated, but how is the battery life on 9A after flashing GOS?
What kind of SOT are you getting and is it any better/worse than the stockOS?