it could be that the client isnt reading your lua properly.
have you tried compiling/renaming it to lub? also you might need to put it inside your grf.
*to make sure it reads it try replacing your poring identity in your jobname.lua with the Arachne sprite
From
[jobtbl.JT_PORING] = "Poring",
to
[jobtbl.JT_PORING] = "Arachne",
just change it back if it changed then we know that lua isnt the problem.
*dont rename the sprite to match poring sprite just the lua.