This is no solution in my opinion as vampire would have the same problem outside the Arena.
I think the ability is OP when it can fully compensate damage taken from an equal unit, which can cause endless battles no matter what.
Secondly I think Vampirism should not apply to Vampires nor to non living things like Defences or Inhibitors/Cores.
I think the best thing would be to rework some basics of this ability.

That is quite a long log of many multiplayer games in a row.
I guess the issue was in the last game?
It contains quite some unusual errors which I not have seen before, but the debug commands can easily break single player games, but in a multiplayer game it is surely way more easy to break things.
So I can not tell if it was caused by using them but it is rather likely, all I can say for sure this log looks terrible :D

Hrm we did address quite many MP issues recently, so I hope it will be fixed either.
Also it seems we might be able to reduce lag issues quite a lot with major Patch 1.5 but this will still take some time.
Before that we will release a minor Patch with many issues fixed.
So I will put this one to complete, but please let us know if you encounter it again after next Patch is out.

I can not see anything special in the log, so the low FPS is not caused by errors at least.

The thing is that we can not reproduce this one.
Did you found any way to get this issue again?
Otherwise we might need to decline this report because it is not replicatable.