List not working! When adding item it saves then creates multiple duplicates of same item.

They have recently changed it so that every time you update a list field it sends an update to update the item. If you have any sort of workflow such as possibly a workflow / flow that takes a file and renames it etc. You're probably getting a side affect of this change where each time a field is modified when creating a new one it's basically triggering new item creates or edits each time.

I would start there, but it's definatley not been a good change to drop on lists like that, should be an option configurable in the list settings for something as drastic as this!