ISC_SOCKET_MAXEVENTS is too small by default
In a couple of KB articles, we recommend increasing it if necessary. (See: https://kb.isc.org/article/AA-00508/0). When building BIND with --with-tuning=large we increase it significantly.
Enough environments encounter the error message "maximum number of FD events ... received" that we have considered increasing the default from 64 to 256 in newer versions of BIND - but have yet to do so.
Is now perhaps the time to do this?
References: