strcat You were of course right about the part "the Auditor doesn't have a record of it". When I performed the tests again I noticed a deviation of 6 minutes, although both devices are in the same exact time zone. I guess since there's no more SIM card in the Pixel 3a XL there was no mobile network to connect to and therefore the time wasn't set properly.
So thank you again for the tip to look at the date/clock. The local tests now function correctly and I learned that both devices need to have the exact same time.