So, I was trying to migrate my project from 5.0.3 to 5.1 and it was constantly crashing referring to some blueprint section. It took me a couple of hours to isolate the problem and finally I managed to locate the exact blueprint AND the exact node in it causing crashes. Meet this little naughty culprit:
I think anyone can reproduce it. Simply start a blank new project in 5.1, create a widget blueprint, create a “Listen to Input Action” node, type any action input, connect it to any event, disable the node, try to compile - bang! Connecting it to any execution pins is not necessary.
I tried disabling some other nodes and it was ok, so for now I think only this one can cause the trouble. Hope it can help anyone trying to migrate like I did.