Here's an idea, but I don't know if it will work.
'In a Nutshell' Version
Temoprarily remove the lua file that is having trouble, remove the offending nodes, and then put the lua file back.
The Long-Winded Version
Go to the affected area without triggering the crash.
Shutdown the server.
Make a backup copy of the world to restore from if this experiment doesn't work.
Change the port to a number only you would know and comment-out all the lines that announce the server publicly to prevent other players from logging in while you are working on this problem. If players login while you are working, they will create things that will be wiped out if the world has to be restored from the backup or they may inadvertently cause more problems to arrise because a lua file will be disabled in the next step. Better to limit potential headaches to just the area you are working on.
According to the log you posted, the lua file that is having problems is the .../minetest/builtin/falling.lua. Create a backup copy of this file, delet the original, create an empty file (nothing in it, no code or characters whatsoever) of the same name 'falling.lua'.
Restart the server and log in.
Try digging the offending node(s). If doing so doesn't crash the server, use WorldEdit to completely remove a larger section of the area (//set air). By 'completely remove' I mean every stone, dirt, grass, tree... everything, leaving a large, recatangular hole in the ground and air space. This is to remove any other offending nodes you may not have found.
Shutdown the server again.
Delete the empty 'falling.lua' then restore the backup copy of the original 'falling.lua' file.
Restart the server and login.
This time, Use WorldEdit to fill the hole with dirt. Then dig/place nodes to landscape the area back to something that looks fitting. Besides making the spot pretty again, you are also manipulating nodes in the area to see if doing so causes the server to crash again. Hopefully not and this experiment has been a successful fix to the problem.
After your landscaping is done, shut down the server again, reset the port to the publicly known one that everyone logs in to and remove the comment hashes from the server announcing lines.
Restart the server, login, and resume the stream project you were working on before this problem showed up.
Hopefully this will work but, again, I don't know. It's just an idea I would try.