Some warrior spiders dont seem to exit lvl 2 or 3 spider den when using a webby whistle. Looks like this bug only happens when some of the den's spiders are outside of it.
Have a tier 2 or 3 spider den
Kill most of the spiders inside it and let some warriors live and hide back into the den (during the day)
When they are in the den use a webby whistle near the spider den containing the warriors that you let live.
The spiders dont come out of the den, and if you or your spider follower attack the den the warrior spiders will finally come out.