User permission issue - major problem

I have a multi company, multi cost center setup. I have enabled strict user permission in settings.

Now, I have a user who only has access to one company, I have also set it as default but he now has two issues-

  1. He doesn’t see any sales orders or invoices because there’s a field ‘represents company’ which is blank unless it’s a inter company order. So, the user now can’t see the orders if this user permission is set.
  2. He can’t save any sales order because, system tries to set his default warehouse in invoice line for field customer warehouse. Why?

These are major issues which now makes it almost unusable for my use case

Have you solved it yet?
If yes, kindly explain why.
If not, could you please elaborate more the two issues, images will make a great help.

in customize form for Sales Order, please check ignore user permission for represents company field

or do not check this

can you provide step by step screenshot and the error screen?