Hi @NianticModKKI,
I just encountered the same issue on Magnamalo Dual Blades, and a friend of mine also encountered the same problem on the Halloween Long Sword.
This rules out the “same weapon type” as the factor.
My friend also did not play with a Switch Axe user during his solo hunts, so that means it’s also not entirely related to other users using the Switch Axe.
However, one common factor between the two of us is that we both had put the app in the background at some point since the last restart of the app (either to use the phone for other tasks or to simply save the battery if we’re on a moving transport and cannot play due to high speed restriction), then we switch back to the app when it is possible to play, and then the issue will very likely occur after completing a large monster hunt and then tap into a small monster (the 60fps mode is not disengaged after the large monster hunt and the game continues running at 60fps even while on the field map and in other screens), especially if we have put the app in the background for a longer period of time (i.e. not to switch away just to reply a message but to have put the app in the background because we cannot play it for maybe 10-15 minutes or longer).
This experience is consistent with the issue of 広域マップボタンや方位磁針ボタンなど、画面の上部がタップできなくなる / Buttons at the top of the screen are sometimes unresponsive, where this issue also often occurs when returning to the app after putting it in the background for some time, except that this issue with the top part of the screen being unresponsive also occurs even at the start the game.
Hope this helps.