[1.20.1] How to get collection of currently loaded chunks?

I need a collection of currently loaded chunks that can be iterated over to check if they contain one of my custom mobs. I tried creating a public static ArrayList and adding and subtracting from it on ChunkEvent.Load and ChunkEvent.Unload respectively, but it keeps throwing a ConcurrentModificationException error, despite me not modifying it while I'm iterating over it. I *believe* this could be caused by two Chunk.Load events firing simultaneously, although I'm admittedly not enough of an expert into Minecraft's internal mechanics to know if this is the case or not. Regardless, if there is a more straightforward way of getting all the currently loaded chunks, I would like to know it.