I know you said you tested in a Private browsing window but can you also try testing in a Guest profile (Menu --> More tools --> Guest profile) and see if you get the same results? Make sure you close your original profile window when testing (so that only the guest profile window is open). Additionally, this could be some weird conflict with an extension you have installed (if you have any) — the guest profile test will tell us more.
Initially dismissed this extension from potential issue as I did not grant the extension permission to the site (only when clicked). Strange that even though I limited the extension’s permission to activate on-click only, it still triggered the issue. Either this is some intended behavior due to service worker or potentially vulnerability bug
Now I tried using the extension on Chromium and immediately reproduced the issue. In any case I’ve removed the extension and no longer had issues. I have subsequently opened an issue with the extension repo