interface freezes, turns white, and doesn’t allow any actions

Hi,

I am a long KNIME user, currently using KNIME 5.12 LST, and I want to report a very frequent issue occurring lately (last 2-3 weeks):

for workflows which where working without issue for quite some time, now, when I run them, hte entire interface freezes, turns white and nothing goes (exept taskmanager).

I have seen that there seems to be a certain relation with loop executions (curiously it happens NOT when the loop is executed step-wise).

Any idea what the reason might be?

Thanks!