I saw the entry in the known bugs post about Plague Mare consuming reinforcements causing soft locks, and this may be the same thing.
My board:
Slimefoot, the Stowaway(4)
Demon of Catasrophes
Grand Warlord Radha
Opponent’s board:
Empty
No supports on the board on either side.
I match 3 to play another Demon of Catastropes. It consumes 1 Slimefoot reinforcement, so I am now at Slimefoot, the Stowaway(3) and soft locks. The second Demon of Catasrophes does not enter the battlefield before the soft lock.
The Battle Log reads
Demon of Catastrophes was cast by [me]
Slimefoot, the Stowaway dealt 2 damage to [opponent]
Slimefoot, the Stowaway was triggered
[I]: Gain Life: 2
Scrolling up through the Battle Log to the first Demon of Catasrophes that I cast this game and it reads:
Demon of Catastrophes was cast by [me]
Demon of Catastrophes was triggered
It looks like the first time it triggered properly, consuming 2 reinforcements from saprolings that I had on the board. The second time, something went wrong with the trigger, even though I had enough reinforcements on board for it to happen properly.
I have used Slimefoot, Saprolings, and Demon of Catastrophes before with no soft lock issue.