I have just managed to recreate the roomba glitch. The error message I got is "Fumo Reimu articleplatform_update.gml[L130,c13] Couldn't find instance '120578'". (If it's of any use, one time the error message displayed 114598 instead of 120578 and L130, c12 instead of L130, c13.)

Thing is, it turns out this is because of another modded character. Probably not near as big of a bug due to that, but it still might be a good bug to be aware of. Basically, my friend was playing as Bandanna Dee ( https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=2134571731 this one I believe) and this character's side special throws a spear which can stick into the ground. Apparently the spear has a hurtbox and when the roomba collides with it, the game has a stroke and the roomba begins to float and move to the side of the screen forever. Interestingly, although the roomba can't hurt anything when the glitch is active, you can still walk on it. I've recorded myself replicating the glitch here: https://streamable.com/3f7hwc