Performance problem from a query in in mdl_comments

After updating to Moodle 4.0, we noticed slow queries on mdl_comments in the database.

These always have the same query as cause:

SELECT c.*

FROM mdl_comments c

WHERE c.commentarea = 'question'

       AND c.component = 'qbank_comment' 

        AND c.itemid = '1234' 

The query came with MDL-71642 for backup of questions in core.

We have now observed the query in production for a few days and see a payload of 25% to about 60% on the database.

The cause for this behavior could be a missing index on

commentarea, component, itemid