errors when moving from PHP 7.4 to 8.1

[catharsis71]

I'm testing migration to a newer server, old server is PHP 7.4, new server is PHP 8.1

On the new server (but not the old server) I'm getting PHP errors in the log when accessing a directory with two .m4r audio files

ipv6-error.log:[Thu Dec 22 19:43:16.765233 2022] [proxy_fcgi:error] [pid 356076:tid 281472808632512] [client XX.XX.XX.XX:65227] AH01071: Got error 'PHP message: PHP Warning:  Undefined variable $duration in /var/www/h5ai/private/php/ext/class-thumb.php on line 427PHP message: PHP Warning:  Undefined variable $duration in /var/www/h5ai/private/php/ext/class-thumb.php on line 427PHP message: PHP Warning:  Undefined variable $duration in /var/www/h5ai/private/php/ext/class-thumb.php on line 427', referer: https://ipv6-test.cracky-chan.com/files/misc/iphone-ringtones/

from the browser/user perspective everything appears to work properly but the log errors imply that something is amiss