I had this several times and It drove me crazy.
Let´s say I mapped dozen shapes and they were ready for the show next day. Ok, I think, "Power off everything till tomorrow."
Next day mapping was gone and I was like... who the hell touched Arena during the night?
I had to do all over again.
I allways thought of it as some sort of Arena bug.
But two weeks ago I was performing, projecting to my "DJ Mapping Cabin", when suddenly some jerk just plug-off the projector power cable during the show. WHAT???
Forget the implications of it... let´s focus in the issue in hands. Power was up and I realized that I could have the very same problem as before, but this time during a show. Oh shit.
I guess I also restarted Arena, dunno why and when it got back on sending output to the projector - damn, everything was gone again. AS YOU DESCRIBED: NUMBERS WERE ALL THE SAME, CORRET, BUT PROJECTION LOOKED DISTORTED OR MISPLACED A LOT. I would have to fix that on the fly...
It took some seconds, no one moved a bit or touched the projector and then suddenly everything got back in place, perfectly. It was just like the projector identifying the current signal resolution whatsoever.
So, now I believe it is a projector issue. I´d try restaring the projector.