I have noticed that there is a php warning when the plugin tries to generate a new cache key. It should be a simple fix. In function get_cache you should check if $exparation is set (line: 134).
Warning (PHP 8.1):
Deprecated: strtotime(): Passing null to parameter #1 ($datetime) of type string is deprecated in /srv/www/hit2023/current/web/app/plugins/wp-rest-cache/includes/caching/class-caching.php on line 135
