Scrolling up through the Battle Log to the first Demon of Catasrophes that I cast this game and it reads:
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.