On a mobile (iOS) device using Safari, when I attempt to edit the tags on a question using the "edit tags" link, I get a pop-up saying "An error occurred when fetching the tag editor". I can use the normal "edit" link to edit the tags successfully. The issue does not happen on a desktop browser.
I'm not sure if this matters, since the pop-up happens either way, but I tried in Safari with both "Request Desktop Website" mode and "Request Mobile Website" mode.
I can reproduce the issue from both a Wi-Fi and a cellular connection on the mobile device. I can also reproduce the issue from the Chrome browser on the mobile device.
I'm using iOS version 15.2.1, which I think translates to Safari 15. I do not have any Safari Extensions installed, and I have not changed any of the "Settings → Safari → Advanced → Experimental Features" from their defaults.
I encountered this issue on Unix & Linux and do not yet have enough reputation points anywhere else to test on another site.
Screenshot of the pop-up: