Windows 10 Pro password trouble

I have brand new 12 Windows 10 Pro 20H2 PCs in my office and i am responsible for them. I set them all up identically however i have 4 that are an issue for me.

These PCs are all networked together, they all have the same username and have administrator rights. The original PCs came with 'admin' as their main user account. These have all been removed. I have set them all to never shutdown, never sleep and I set the sign on option so that they don't have a password. ( The PCs need to be on 24/7).

However 4 of the PCs (every 4 weeks) gets a pop up message;

"your password has expired & must be changed"

I click 'ok'

Then the pop up come up to enter a password in the 'new password' box

i hit return

Then a popup appears "your password has been changed".

So does anyone know how to get rid of this?

Regards