koreader/styletweaksto mass disable them, and it hung starting after a reboot on a different epub, the whole of which I was reading thruoghout last week. My question would be now if I can make the logs more verbose than the -d flag and whether it would make any sense ;)
Also quite odd is that (naturally) @houqp, @poire-z, myself, and by now presumably plenty of other people already tested those changes.
You could make the logs more verbose for crengine specifically by recompiling it with DEBUG_CRENGINE (see https://github.com/koreader/koreader-base/blob/f549ca8922f92a70986082a1d2023de3e7cd9a68/cre.cpp#L2823-L2826) but other than that not really. It is however quite easy to do some gdb remote debugging, to the extent that you know gdb anyway.