On our server, we are running Spigot 1.15 Version 2570 (Tried 2571, but installation failed time and time again). After creating a Wither Skeleton Farm, we noticed the the Wither Skeletons are not effected by the wolves at all. So to be sure it's not a 1.15 change, I went into my personal creative world (1.15) and recreated the scenario (Completely Vanilla) and the the skellys run for their lives! Any help would be greatly appreciated! FTR, we are hosted by CubedHost.com
So I tested on vanilla, CB and Spigot (2574) ... all three scenarios the wolf chases the wither skeleton, and the wither skeleton runs. My guess is you maybe have a plugin that is stopping this from happening.
It's probably Bedrock Killer, all the others plugins shouldn't interact with that kind of mechanic. Try removing and see if it is fixed.
Sorry for late update. Removing bedrock killer did not work. We are currently attempting to get version 2571 of Spigot installed but having issues through Cubedhost. At this point, it's the last thing we can really lean on. EDIT: We are on the latest version available on Cubedhost now (2574) and it still doesn't seem to be working correctly. We are left clueless at this point.
Try disabling all plugins by renaming the plugins folder to old-plugins and starting the server. See if it fixed
