Options set in /etc/resolv.conf affect dig behavior during system tests
In BIND 9.11, where liblwres is used for parsing /etc/resolv.conf, certain options directives affect dig's default settings. Namely, timeout and attempts override the defaults for +timeout (5 seconds) and +tries (3). Depending on the values of the options set in /etc/resolv.conf, system tests assuming dig's default settings are in effect may fail.
I do not think this is a bug in dig. At any rate, changing the aforementioned behavior in BIND 9.11 would mean introducing a functional change in an ESV release.
BIND 9.12+ uses libirs instead of liblwres for parsing /etc/resolv.conf. Since libirs does not process the aforementioned options directives, BIND 9.12+ is not affected by this issue.