Tested with new stable release (v3.5877). But still a no go. You don't get an "event saved" acknowledge anymore.

I found out that adding an "else if" in combo with logic "=" or logic "set" is a bad combination to save the event. Starting a new event drag "if Do Else If" to build field and add new "else if" blocks. Save event will work, no problem. When adding a logic "=" to first If. Event will not save ...

I have exactly the same with latest stable release (v3.5837). A bug that survived several stable versions. Will try the workaround.