OK, I've encountered quite a few alien civilizations during my playthrough (Precursors, Swarm and 5 different NPRs) and at some point I suddenly stopped accumulating diplomatic points with the last encountered NPR. I initiated communications, their language was translated, the diplomatic rating reached 26 points and then it looks like it stopped - I don't recall if I did something to cause that myself or not, because I probably didn't notice it right away. I should mention that diplomatic points with the 3 other NPRs rise normally (I am at war with the fourth and more or less obliterated them). I also don't get an intelligence update about diplomatic contact with this last race, like I do for the other 3.
First thing I did, was I checked if my diplomatic ship has active sensors turned on and if she's in contact with the alien ship and everything seemed to be in order - my diplomatic ship was parked on the same spot as their diplomatic ship and the AS were turned on (and yes, my ship has a diplomatic module and their language was translated). I checked if perhaps the sensor detection in the system is turned off through SM and it wasn't, neither was the DR fixed by SM - I even tried freezing and unfreezing it.
The next thing I did was I sent a different class of ship with a diplomatic module to their diplomacy ship and still nothing. So I decided to send my diplomatic ship into one of their systems, just in case alien diplomatic ship didn't have active sensors or something similar (I mean hey, I suppose I could encounter a race of dumbasses - I see no reason as to why us humans should be unique in that regard
). They seem to see my ship all right, since I immediately started getting an alien communication requesting I withdraw my ship, but the DR still doesn't change.
I should mention, that I turned Swarm off, sometime while the campaign was already running and instead turned the Invaders on - I actually thought I encountered the invaders when I first met this race, since their ship looked rather unique (like a very aggressive flower blossom, I suppose?) but considering their name seems to be Empire of Port Lincoln, I don't think that's really the case.
I still haven't encountered the Invaders though.
I am at bit of a loss as to what else to try, so does anyone have any suggestion, perhaps even encountered something similar or have I by chance encountered a bug?