Then I don't know what happened. I have upgraded to LineageOS 16 based on Android 9 and now I can use it again. So the problem is solved for me. Thanks for the reply and have a great day.
I can no longer find swiftkey in Google playstore. Have you stopped supporting Android? I use LineageOS 15.1 based on Android 8.1.0 and I have been able to find it and update it until now. If this ...