When disabling slow query log rotation by reversing the steps described here, the new value of `slow_query_log_file` is ignored until a server restart. The old file handle with the sequence number suffix remains open, and the correct file handle is never opened.

Start server with:

Enable slow log rotation:

Verify that file with sequence number suffix is open:

Now reverse steps to return to default slow log configuration:

Confirm old file is still open:

Just to make sure, disable and enable the slow log:

Old file handle is still open:

After a restart of mysqld, the correct file is being used: