Up to Patch 3.0 a lot of events had - outside of specials - extremely static spawns so that you could stop on a watch when which enemy would apper from where. This has however been broken down in smaller segments to make events feel more randomized as people complained about static spawns. It is not specifically mentioned in the listed Patch Notes, however, it was mentioned in the Developer Update - May 8 - Announcements - Fatshark Forums (fatsharkgames.com).
To your specific points:
Can’t say assassins spawn regularly for me. This is rng.
This change has happened with the Grail Knight update. The event is still pretty static for the most part but the order has changed here.
Chaos Warrior Wave is and always has been random. They never changed anything in that regard. You could get it all the time. Just another case of rng. Sometimes you get them, sometimes you don’t. The only changes to the event to my knowledge are: explosions in final phase no longer damage bots, nurgle flies being slower and I think the spawn drops from all four windows during his invincibility phase so that not 8 Chaos Warrior jump on your head.
Not sure how they define end event but here from Patch 3.0
As said in the Developer Update the events in general have been a bit more randomized.