Had this problem in 1.11.0.7 (win 10, survival, normal difficulty, vanilla) with both cave spider and skeleton spawners. Also noticed a lot of cave spiders spawning outside of the spawner area, even in lit corridors. Some areas were more problematic than others, like a couple corners of the mineshaft spawning 9-10 spiders every few minutes.
Have the same issue on Beta 1.11.0.5 (win 10) with the vindicators that spawn on woodland mansions. No issues with egg-spawned and raid-spawned vindicators. Difficulty was on hard in all cases, and the worlds were 100% vanilla.
I was on normal difficulty. Also forgot to mention thar killing multiple patrol captains didn't affect the number of waves.
Seems like this is partly a feature, as the Java edition raids now work in a similar way. The number of waves you get has increased and is now difficulty dependent. But the level of the bad omen effect still doesn't affect the number of waves, which I believe it should.