Yes, we all know that you get offered a SL mission every time you complete 15 regular missions of the same level and accept a 16th.
My query is whether the missions have to be of an allied faction for them to count towards the 15/16? It was my understanding that this was not the case (e.g. that the SL counter counted missions irrespective of whom they were being run for). However, I have just done 14 missions for one faction, hopped over to an alternate (non-allied) Faction to do the last two missions, but after having done six now without an offer, am stuck wondering whether there is a bug, or whether I have misunderstood how the SL offer mechanics work.
Wondered if anyone could enlighten me.
 they are all bog-standard Level 4’s, no cosmos, epic-arcs or FW missions and dotlan confirms there are multiple SL agents nearby