With latest version I have these problems (some of them present also on previous versions):
1) With some PDFs koreader exits (crash ??) when I set a bookmark (aka click on upper right of screen).
Only some pdf, with mostly it works
2) Some comment icons not appear (pdf) but others are correctly shown
3) Sometime (rarely with more recent versions, more frequently with older ones) it seems to hang, but not after an idle period but after a click to execute an operation (i.e. on a click to open PDF, on a click of some other type).
It is not freezed only very long time to process an input event (as i have already told here:
https://www.mobileread.com/forums/sho...&postcount=294).
If you have patience it is possible to close cleanly koreader using touch events (it reacts at about one click event processed every 1.5-2 mins, so you need 6 to 8 mins to close, 4 clicks, koreader and relaunch it from start menu).
This under Kobo FW 3.3.0 (Aura HD)