There is a bug with Magic Arena failing to recognize a player can tap their Howlsquad Heavy for mana when you have Max Speed. It is easiest to reproduce when all lands are tapped out and you have mono red cards you can cast that cost equal to or less than the number of goblins on the board that you control.

When Howlsquad Heavy is on the board, untapped, and does not have summoning sickness, the game is incorrectly passing priority to the other player through all phases when your lands are all tapped out, even when you have cards you should be allowed to play by tapping Howlsquad Heavy to produce the mana needed to cast said spells.

But the game fails to stop when you have priority in said cases, denying you ability to use your Howlsquad Heavy's mana production ability, even when you have Max Speed and Howlsquad Heavy is untapped and without summoning sickness.

In my last game, I had a Howlsquad Heavy on the board, along with two 1/1 goblin tokens, a Searslicer Goblin, and Impact Tremors. None of my creatures had summoning sickness, and I already had Max Speed from previous turns. I tapped all 5 of my lands to cast Banner of Kinship (choosing goblins) during my first main phase. The game then immediately went into start of combat phase, despite me having cards in hand that I should have been allowed to cast before combat by using Howlsquad Heavy's Max Speed mana ability.

I attacked with the 1/1 goblin token that Howlsquad Heavy created, and it died in combat. I was not given an opportunity to cast anything with instant speed during the combat phases, despite the fact that I should have been able to tap my Howlsquad Heavy for 5 red mana.

After combat, I was in the same board state as before combat, with my untapped Howlsquad Heavy, two untapped 1/1 goblin tokens, and an untapped Searslicer Goblin, and the Banner of Kinship with 4 fellowship counters.

After my combat phase, I should be able to tap Howlsquad Heavy at instant speed during my second main phase to produce 4 red mana to cast cards in my hand that cost mono red cards in my hand that cost 4 mana or less. However the game proceeded to automatically skip and pass priority through all phases, ending my turn and through the other players turn, despite me having cards that I should have been allowed to cast if it had stopped correctly to allow me to tap my Howlsquad Heavy for mana.