Thanks, @Andrew_Rowe.
The way I read the issue Serial ports getting blocked after some re-connecting · Issue #1842 · openhab/openhab-core · GitHub , this could be a probable cause of my problem as well. This also means we might just have to wait for an update of NRJavaSerial 5.3, correct?
I read of various workarounds (e.g. here and here), but the best option for a semi-experienced User like me is maybe just wait and deal with it and, in the meantime, just re-create the openHAB container every time the problem occurs, correct?