I'm not exactly sure what happened, but my N'Kari campaign was completely ruined after patch 5.1 came out. 

Literally the day before I was making around 20k favor (after upkeeps) and after patching it tanked to -23k a turn. 
For whatever reason the army upkeep shot up to -48k a turn, and my vassals are only giving me 62 favor a turn. 

Even with all my armies, heroes, and disciple armies, the number don't add up to me. I didn't have and still shouldn't have an army upkeep of -48k. 

Did I miss something or is N'kari bugged?

Very confused and frustrated since I was right on the cusp of getting the achievement for winning with slaanesh and really don't want to start over. 

​Hi there, devs have said that the issue with vassal income affects older saves only - this issue shouldn't be present in a fresh campaign. We suggest rolling back to an older beta. If this issue continues to affect you on a fresh campaign please let us know via the Bug Forums, and apologies that this issue has come up for you. Best, CA_Nova