Author response

The error mentions capital S whereas in the English source code I definitely use a lowercase %s as the "format specifier" and I develop on PHP 8+ and have never seen this error.

Judging by the fact that you have loco translate installed, here is what they have to say: https://localise.biz/wordpress/plugin/faqs/printf-errors

This is the core code from problematic line, finely executable under PHP 8: https://onlinephp.io/c/523c4 If you change %s in the snippet to %S then the error you mentioned occurs. That can only happen if the translator (human or machine) messed it up. I believe the problem happened on your end, since JIG has no official German translation yet.