Thanks for the report :)

I think what you are experiencing is related to the lag. When you click the remove an event, it will always make the event disappear in the sidebar on that page, but it's actually sending a request to Subeta's servers telling it to delete the event. This request is probably timing out sometimes instead of completing successfully, because we've been having these errors. So the problem is still fixed, it's just a connection error right now as far as I can tell.