So after creating a second Windows admin user and changing Jenkins to log on with that user, after reconfiguring everything to build there, it worked once. Then, the error started occuring again. I finally found out about the -IgnoreCookErrors flag from UAT and started using it and it worked.
Now, after multiple successful builds, the error doesn’t even show up anymore for some reason. So I have removed that flag again.
I will keep monitoring it but if the error occurs again I will just use the -IgnoreCookErrors flag even though it isn’t a long-term solution.