Ok, that was a long shot. Anyway, if the problem started to appear between 4.20 and 5.0, the easiest would be just to bisect it. Would you be able to do that? If we found the offending commit, it would be easier to fix it (or to force upstream to fix it). Just to be sure, could you also try the latest TW kernel, please? Kernel:stable project in OBS (you might need Kernel:stable:Backport due to some recent incompatible changes. I am not sure.).