Actually was about to post the very same thing,
So i spent the entire night tonight looking for combat missions in particular. The entire night and i found a total of 3. Some people might see a lot of missions, but actually what I see is mostly empty boards, 8 or 9 NPCs with at least half of them saying 0/0.
Or a really random collection of missions, like Source and Return seems a hugely over popular one. Or you hit a station that has nothing but 100+ Mining missions, but actually mostly EMPTY voids of mission boards.
Some quick things, when i found EMPTY mission boards, the station was NOT in lock down. This happened on both surface and stations, and it seems for me at least a VERY Common thing, in truth I saw more blank boards after 5 hours of playing then I did pick up missions.
Another sign that this is not just an illusion, is the fact that people are literally doing Videos and lets play of where you might find missions because frankly they are like gold dust.
A game system should not encourage players to log out and back into instances, not that it helps much in my opinion anyway unless you find a functioning station. If i find a station board that works as it should I tend to stay around there, doing missions as intended, but what I have also found, is they quickly BREAK.. not simply change, but actually start behaving really strangely for instance, NO MISSIONS at all, Couple of hours later, NO MISSIONS AT ALL, couple of hours later, 100+ Mining missions followed by NO MISSIONS AT ALL. Its like it just goes nuts.
Another issue one thats even worse. Is delivery boom missions, or any delivery, where NPCs suddenly vanish off the boards making you have to abandon missions... if they happen to be wanting to go to that particular NPCS, and no amount of changing instances, logging out or leaving it a day+ (until the mission nearly expires) changes it, it simply keeps telling you to hand it in to the broken station.
So to the OP, I totally understand what your talking about, for me tonight has been a complete bust... I have been unable to play, because frankly I wanted to combat, and that was absolutely not to be today, unless I went into a res, or some other none mission thing. But thats "Space" as Commander Thane would say.. I wanted to improve faction, gain some credits, earn points towards combat elite, and fly my newly fitted corvette. I did not want to mine or do boom data missions (which tend to have the same issues anyway)
Very disappointing, Very frustrating