Posted about this over here:
https://us.forums.blizzard.com/en/wow/t/venari-maw-upgrades-not-working/754729/2
TLDR: The Jailer’s Mark ticks up your Eye of the Jailer every time it ticks after application, making Assassins and Abductors double-punishing to your time spent in the Maw. The upgrades from Ven’ari are working as intended by removing this double punishment. Read the item tooltips closer.