Printing to Windows (not-domain) Server - Hold for Authentication
I'm not sure how helpful this will be but I offer it in the hopes it will generate an idea that might work.

On a Macbook Air with Mojave I usually map directly to the printer via IP Address which is the second icon from the left in the "Add" (printer) dialog box. I find this to be more reliable than printing via our print server which is one of our Active Directory domain controllers.

However, once you select the print server (in my case it is [DOMAIN NAME] > [Print Server]) it pops up an authentication dialog box "You are attempting to connect to the server "[SERVERNAME]" Click connect to continue"

Once you click connect you get a standard login dialog box with your username already filled in.

Don't use that username or your local password there

Instead you need to enter the name of the print server, sometimes referred to as the NETBIOS name, followed by a backslash " \ " and then a username of an account on that particular server. In my case it would be something like this:

domain\stevec
[password]

In your case as you are not in an AD domain:

servername\username
[password]

Windows expects authorization from outside the domain to be fully qualified. EG where the credentials are, a backslash and then the account/user name.

It could be that when you try and print there are cached credentials somewhere (possibly on the server?) that are messing you up.

I would delete the printer queue from the Mac and re-add it via the Printers &amp; Scanners preference and choose the Windows printer option and logging in as a user on that PC.

Either that or select the "Default" or "IP" methods and completely bypass printing via your Windows server, if that is possible.