Encountered this just last Sunday on Switch v6.2.0 (r33694).
While grinding out the daily Boss Dungeon, I made a normal match that set off a combo including a Lycanthropy Gem and an Extra Turn, then immediately cast Banshee’s “Scream” against the sole remaining opponent (a King Mimic). During this process the Lycanthopy Gem was still floating its way across the board, and it seemed to disable King Mimic as a valid target, softlocking the game with no responsive UI elements at all (even the Menu icon in the corner is disabled).
Screenshot (I also have a video capture, if needed)
I can also confirm King Mimic WAS shown (very briefly) as a valid target before the Lycanthropy icon appeared on its card.
I had no recourse but to switch (no pun intended) to my Home screen and close the software manually. I typically play this game in handheld mode, using touchscreen controls.
This looks like something that could theoretically happen in any game mode assuming it can be replicated (my particular case involved a combo with new-gem RNG, but any 4- or 5- gem match involving a Lycanthropy Gem would make for an easier testcase).
Never disable the Menu icon in the corner.
For spells with manual (ally/enemy/gem) targeting, add a “Cancel” button somewhere onscreen. There have been prior cases where I was clicking so quickly to cast a spell I didn’t realize I clicked the wrong ally and ended up casting the wrong spell.
It might be related to that last one because that also involves a combination of:
Spell that manually targets an opponent
Special gem types (Lycanthropy gem, Cursed gem, etc.)
“Playing at a fast speed”
Notably, in my case King Mimic WAS highlighted as a valid target when I initiated the spellcasting, but became disabled upon contact with the Lycanthropy Gem, creating the softlock. Which all happened during an interval of about 0.2 seconds so it’s very good I caught it on video:
Before - note the Lycanthropy Gem is still traveling (see row 7 column 7) and King Mimic is a valid target