**Update: WordPress 7.1 issue fixed by changing Field Group IDs**
Quick update on this issue.
The HTTP 500 error on my Meta Box Settings Page under WordPress 7.1 was caused by Field Group IDs containing Japanese characters.
I changed the affected Field Group IDs to English/ASCII IDs, and after updating back to WordPress 7.1 the Settings Page now works correctly again:
* page loads normally
* tabs work
* Save button is present
* no more HTTP 500 / PHP fatal error
My Settings Page ID remains:
nss-option
There is still one remaining issue: switching between tabs is noticeably slower than before, around 1 second per tab change, whereas previously it was almost instantaneous.
I tested the tab switching on WordPress 7.0.3, 7.0.4 and 7.1, and the delay is present on all three versions.
So the WordPress 7.1 fatal error is resolved, but the slower tab switching appears to be a separate issue.
Thanks to Meta Box support for pointing me in the right direction.
