@trendoscope
Hi. All the Publii theme upgrades I’ve done tend to work first time. Though to test, I too have just done the same upgrade using a test website. Worked fine with no problems both in Preview and live test: the actual upgrade took about 10 seconds (using the current latest Apple MacOS ( Ventura 13.5 (22G74)). Though after upgrading themes, I tend shut down Publii, wait a few seconds, then restart.
Without more specific information, it’s impossible to help further.
Are you using Microsoft Windows or Linux OS?
Have you got any theme overrides?
Are the errors you’re getting when viewing in Preview or when checking your live / draft website?