negative influence
 

I think I have this only after getting patch ...14 from Steam. Sometimes my influnce drops to the negative numbers way down, like -121 million. Largest drop was to -1.x billion. Also the bar on the bottom-right graph displays it to the left. My char is a level 64 warrior (loner challange) if it is important.
Sometimes it jumps back to positive, later on.

That sounds like an overflow issue which I thought I had fixed these. Were you getting close to 4 billion influence?

I think the same: overflow issue. Maybe the increase itself is unexpectedly big. So far I see it happens also with other covenants as well, not only with the player (me).