It seems like after each update, there is an issue with zeds spawning. I remember when the hellride map was released, scrakes would not spawn, and gorefasts were spawning like weeds. Now it appears that crawlers spawn like crazy. Now, my thinking for this is because we all know that the zerk's counters, are between a long distanced husk and a swarm of crawlers. So, maybe the crawlers spawning in larger numbers, is an attempt to make life for the kiting beserker, harder.
I don't always kite maps, but when I do, I make sure to either perfect my timing in swinging at crawlers, or I bring a handcanon with me.