Me too. Don't even have to log in. As soon as I click the "?" in the upper right the MTGO client instantly closes (and is gone from task manager) with no error message of any kind. The good news is I never once clicked on that icon until I was trying to reproduce this bug 😂.
Seriously, it doesn't even need to be that much. As many players take the Vintage Cube season very seriously, it would be nice to see a little appreciation from WoTC. Maybe minor prizes for the top 10 or whatever, and something cool for 1st. A respectable number of play points and maybe a...
It looks to me like the MTGO client is just putting the creatures into the graveyard before the "whenever this creature deals combat damage to a creature, exile that creature" trigger resolves (it does show the pop up for the trigger, but does nothing because creatures are already in gy)...
This is only really a Vintage Cube issue as far as I know, but we use it for our own cube that we play regularly and would appreciate it being fixed for Turnabout/High Tide shenanigans.