Mysql server running as replica doesn't record the slow queries in the slow query log, even though it's enabled

I am running a MySql 8.0.29 server serving as a replica for another server on an ubuntu 20.04.4 LTS box. 'slow_query_log','ON' 'slow_query_log_file','/var/log/mysql/mysql-slow.log' 'long_query_time', '10.000000' I ran a query that took approx. 20s, however, the query doesn't show up in mysql-slow.log. The file is empty (size 0). Any ideas where I can look to find out why the query is not recorded in the slow log? I checked the error logs, and syslog and there is nothing related to this. File permissions are ok as well. Thanks Update: it worked for a while after flushing the slow log, then it lost it again. Not sure what it is...