I've started numerous campaigns and have 6 vassals currently who never make an attempt to come to me unless I literally come and find them on the map.
My relations with them are all 70-100 so they trust and like me.
I've tried "gather our forces" in the kingdom page as well as by having my companion declare that they should come meet me.
I've also sent messages from my court man to my vassals to come find me and usually the messengers don't make it or they reply with no (but always say yes when I come find them)
I assumed it was because I was in Essos and most of my vassals were in Westeros, however I've now spread everyone out a lot more but they just simply won't come when called.
Any ideas?
compare your renown to your vassals. they're not gonna follow you now matter what , if they have higher renown than you.
Happens to me too, and I have the highest renown of any character in my save game. :-\
could be they dont have enough troops.
Happens in the base game and other mods too. The best I could figure out was that the further away the lord is from you the more likely he is to ignore your summons regardless of relation score, which seems to jibe with your issue. In that case you have to go find them and have them follow you.