I have an old world that I have been playing on since 1.14.4 and in this world I have old witch huts, ocean monuments, and neather fortresses. Recently I noticed that they stopped spawning the mobs that they are supposed to spawn. I thought this was odd as they had worked in the past on this version.
My fault. Details in comment.
Upon some investigation and experimentation, I remembered that I had at one point updated this world to 1.18.2 and then immediately backtracked this update. Going back to a backup I made before reverting, I have found that the structures mentioned beforehand are unaffected. I am therefore lead to believe that this problem I reported is my fault and should be resolved.