I think we have the same issue here, but game is unplayable for us now and will freeze for minutes or be 1fps when it returns.
We started having these small freezes / stutters every once in a while after being in the fort for a little while, and the freezes would get slightly longer every time it seemed. Eventually we would all get a message that our game had stopped working, but if we just waited it returned after a while, so we thought we could just play onward. Then after we got back to the fort having killed the crocs on the beach, the problem had progressed to the point where the game was unplayable. Our computers would also go nuts, crash, get artifacts in other programs and I noticed the physical memory would fill up slowly until it got to 98% usage in task manager. Its as if something is constantly building up taking more and more RAM whenever we got close to the center of the fort area by the waypoint shrine or the little kitchen/hideout with griff and his crew.
Eventually we reverted to a really old save, where the problem was not present, but after having played here for a while again the problem has returned and is just as bad.
And yeah, quickloads will almost always crash the game if we haven't restarted in a while. Didn't think it was related to this issue but if the same happens to you..
Only "out of the ordinary" that we have done to the save are transferring the savefile from my friends to computer to mine at an early point in the game, however we did this cleanly as suggested by staff in another thread by going into documents and copying the save folder under Profile>Savegames>Story, so that shouldnt be an issue? We did a great deal of theft in the city by turning all the npcs around and stealing their stuff, could be related to AI going crazy looking for culprits?? Doubt it but am just listing everything.
Also, the further the issue has progressed the longer the loading times are.
Definitely not something related to our computers as we are all having the exact same problem with very different specs.