I think I know what's going on. The pick filter function is being called for entities it used to not get called on, like cameras or pivots, anything with a pickable subchild. The parent probably does not exist.
So your filter previously had sort of an error, but the engine didn't make it come up. And it's not really necessary for those entities that are currently causing the error.
The solution is I will fix the behavior in the engine, and you should fix your code to make sure a parent exists. Always write code with error checks like that, and you will save a lot of time, with any programming SDK.