A couple suggestions: close project of you will be away for any length of time. Project doesn’t seem to do well being left over for a length of time. You might want to try using the inspect function to determine which task is causing the problem. I didn’t have the same situation as yours, rather when I kept leading back to the same activity after several paths of using the inspect function. When I discovered the culprit, I copied the task and pasted it right below, then deleted the original task; the problem resolved. Obviously, there was something corrupt with the original task. Finally, if you ever try to save your file and you get the jumbled screen and/or it sits spinning, then that is likely when your file becomes corrupt.