I tested the eoan kernel 5.2.0-10-generic and the suspected problems in the block layer didn't happen anymore after removing the workarounds (artificial delays and module insertion) needed by the bionic kernel 4.15.0-54-generic used in core18. 5.3.0-050300rc4-generic also works without any immediately visible problem.
I tested the eoan kernel 5.2.0-10-generic and the suspected problems in the block layer didn't happen anymore after removing the workarounds (artificial delays and module insertion) needed by the bionic kernel 4.15.0-54-generic used in core18. 5.3.0-050300rc4 -generic also works without any immediately visible problem.