"must attack if able" + "can't attack unless you pay" effects results in being unable to attack

I couldn't find another issue already opened for this.

Bug was observed with Thantis, the Warweaver and Koskun Falls on the battlefield in 4p EDH. I assume it works the same with other cards that provide the same effects.

Reportedly you were unable to attack the controller of Koskun Falls, even though you had enough mana to pay for any potential attackers.

Edit: Have tested a bit more, and it does the same for Propaganda and the white taxing cards.

Also if you add Goad into the mix, so you're unable to attack someone, but the rest have propaganda effects, the game is unable to continue past assign attackers.