Sparky Freezing at 10+ Creatures
Sparky now freezes on AI's "declare attackers" phase if the AI controls creatures that are able to attack, and there are 10+ creatures on the board total, combined between player and AI.
At 9 creatures (combined), there is a brief hiccup in the "declare attackers" phase, and at 10 (combined) or more, Sparky will lock up and time out.
Distribution of creatures on the board is not important, it appears to happen regardless of number of controlled creatures on either board, once that number reaches 10. Other permanents on the board do not count towards this limit, including artifacts, enchantments, or other alterations to the creatures themselves, only total number of creatures. Token creatures are counted towards this limit.

-
Allirog#15154 commented
I suspect this is programmed to do so in order to discourage folks to play against him as it happens on all platforms. Never payed attention to "when" it freezes but I'm pretty sure that I saw freezes with less creatures on the battlefield i.e. like 3 vs 3.