Mobs not spawning during Raid

I run a server on 1.14 and I've been having this issue ever since we updated-- on occasion, the hostile mobs involved with a raid won't spawn. The villagers will still behave as if a raid is going on, but there's no one attacking.

I can command kill the mobs, so they're there but they aren't showing up. I'm uncertain if anyone else has had this issue-- I am running Bukkit 1.14 and I'm wondering if that could be responsible, but we had the same issues with the server on vanilla.