Bug? UUserWidget is GCed even I have a reference to it?

I have two UUserWigdet pointers in LevelScriptActor. It works fine for a few minutes, however, if I keep game running for a few more minutes and I add them to the viewport. It crashes with access vioation. Does that mean the Widgets is GCed? Why they are GCed? Aren’t UObjects got GCed only when there are no reference to them?

@Knight419 could you post your code?
Are your two UUserWidget variables UPROPERTY? but anyway, with the code it will be easier to help.