a bug was found in how the clients-per-query code worked with some query patterns. This could result, in rare circumstances, in having all the client query slots filled with queries for the same DNS label, essentially ignoring the max-clients-per-query setting. It is fixed in 9.4-ESV-R5, 9.6-ESV-R4, 9.6.3, 9.7.3, 9.8.0 and all superseding minor revisions and newer major versions.
3009. [bug] clients-per-query code didn't work as expected with
particular query patterns. [RT #22972]