This is currently being investigated.
Just as a heads-up, I have a little more information that might be useful. I actually just wrote up a support ticket and sent it in:
A repeatable bug (reproduction rate: 100%) occurs in the Cliffsides fractal that renders it impossible to complete and forces a complete restart from the beginning of the scale. This kind of run-ending bug is unacceptable – especially in a tediously long and unrewarding (thanks to the infinite respawn = no loot enemies and fighting the final boss TWICE) fractal that shows up as a possibility for both the 2nd and 3rd, making it one of the most likely fractals to show up in a given run, at ~36%.
The glitch results in the Cultist’s Hammer disappearing from the map and becoming permanently irretrievable.
The glitch is triggered when the hammer carrier falls through the cracks in the platforms around the ARM seals of the colossus, right before the boss of the fractal. In my personal experience, I’ve only seen this happen at the arm seal closer to the boss, but the reproduction rate is 100%. Every single time the hammer carrier falls through one of these small holes around the arms, the hammer vanishes permanently.
My personal suspicion is that this occurs because when players fall through those particular holes, they are immediately placed in the downed state on the VERY SAME platform. With most falls off the level, the player is placed in the downed state at the hammer pedestal of the PREVIOUSLY COMPLETED platform, but with this particular location (and possibly others, I haven’t tested outside of the arm seals in particular) the player is placed in the downed state at the hammer pedestal of a NOT-YET-COMPLETED platform. Since the platform is not completed, the hammer cannot be placed at the pedestal where it should, but is glitched to only be able to spawn at that platform, causing the hammer to be effectively completely removed from the map.
With some of the hammer disappearance glitches on this map, a full party wipe is enough to respawn the hammer at the pedestal of the PREVIOUSLY COMPLETED platform, but perhaps because this glitch seems to bind the hammer to the pedestal of a NOT-YET-COMPLETED platform (where it is impossible for the hammer to appear), even a full party wipe does not make it possible to retrieve the hammer. Upon full party wipe, and simultaneous respawn, the hammer appears briefly (about 0.25 seconds) at the pedestal of the PREVIOUSLY COMPLETED platform, but it disappears immediately afterward, rendering it permanently irretrievable. I’ve tried many combinations of various tactics to get the system to respawn the hammer at the correct pedestal, but to no avail.
Attempted fixes: Full party wipe, full party wipe with everyone respawning except hammer wielder, everyone leaving fractal (character select) except fractal opener, various combinations of player suiciding and staying alive at pedestal, and none of them have worked. To my knowledge, there is no current solution to this gamebreaking bug, which forces a complete restart of the entire fractal run from scratch. This bug has occurred 6 times for me so far, and has a 100% reproduction rate. Every time that a player with the hammer falls into those holes around the arm seals, the hammer has permanently disappeared and forced a restart.
It would be reasonable to assume that any time the hammer-carrying player falls into a location that causes them to be downed at a not-yet-completed platform, the hammer will become irretrievable. For the holes around the arm seals, it’s 100% failure, but I haven’t tested around the chest seal etc. at all, though I do recall being downed behind that little bonfire by the chest seal after falling through a small hole in the chest seal. For this reason, you’re generally safe falling off the windy platforms, jumping puzzle, etc., but you’re very much at risk when near un-shattered seals.
~ Entropic