See the character sheet attached, creature has 6 arms and is attempting to wield 3 longbows using the Multiweapon Fighting feat, but only the single primary attack shows.
Please include a pcg to reproduce the problem. What is the expected output?
Away from my computer atm, but it's pretty easy to reproduce.
Make a summoner. Give it a few levels so you have a decent number of evolution points.
Create the eidolon companion. Choose whatever. Give it all the limbs.
Have it take the Multiweapon Fighting feat (which it now can take since it has more than 3 arms), and try to equip weapons in them.
Expected output is that on a full attack, all weapons are attacked with, but at a -4 penalty due to the multiweapon fighting feat.
Maybe I'm missing something, but when I try this, I can equip one bow into Primary/Secondary, but then can't equip a second bow (which isn't correct, but may be related to what you are seeing)
So net is I am unable to reproduce what you are seeing.
My experience seems to be related to