Unable to respond by tapping a mana producing creature for mana in order to prevent it from being forced to block.
I lost an event match because i was forced to block with a mana producing creature instead of being given priority to tap that creature to add mana to my mana pool. The other player cast a spell that had haste and had to be blocked and arena automatically entered the combat step after that player cast it. The player attacked with all creatures and i was forced to block with my mana producing creature that i needed to be able to cast spells on my turn and win. I was not able to respond to the creature entering by adding mana. I was not able to respond to declared attackers by adding mana. Full control automatically toggles off as phases end so i was forced to block instead of being able to respond with full control. Priority should never be automatically skipped for mana creatures. Mana producing creatures should not be lumped in with lands for possible plays. Arena should have an option disable passing priority for no possible plays and creatures producing mana should always count as a possible play. An option to have full control always active should exist. This would have never happened in paper.

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FireFox31#79637 commented
This is also happening to me. Arena does not pause to give me priority when my lands are tapped but I have creatures available to tap for mana to cast the spells in my hand. I'm not given priority before entering combat, during combat before declaring blockers, and more.
This may be a problem with "This Town Ain't Big Enough" which typically costs 5 but has an alternate cost of 2. I have been denied priority with this card in hand and two mana available, one or both coming from creatures. However, I believe the problem has happened with other spells without alternate costs.
My solution is to enter permanent full control by pressing Shift + Ctrl before I end my turn and start the opponent's turn. This makes for a slow play experience.