It’s a known issue and the Devs are aware of it. I have had the problem in the past and, as it hasn’t been 200ft in either direction and stalled, it has still be there. It is not a matter of pilot error, but of an unbalanced autopilot that still hasn’t been corrected.
some people don’t fly a plane properly and then say its a bug or glitch, the A321 had an actual issue which was fixed in a previous update, as for the 777-300 the answer is simple when getting close to the cruising altitude reduce v/s to something like 500 fpm do it gradually, lets say my cruise altitude is FL350 when i get above FL200 my v/s will be at 2000fpm as i pass FL300 i reduce it to 1800fpm and then 1500fpm, 1200fpm, 1000fm, 800fpm, 500fpm, 300fpm etc,… thats how i do it on the 777 and i never experienced a stall on the 777 in the sim.
i play IF on two devices one is an old Tablet the other is Ipad 6th generation, i flown pretty much all the heavy aircrafts on long haul and ultra long haul flights and the 787/777 are the best i never experienced a stall on a 777 or 787, the other day someone made a topic about the a321 pitching up & down violently during approach at 3000ft i quickly tested that and find out that the pilot set the speed a bit slow therefore the AP was pitching up trying to maintain that altitude,.
many things like stalls happen due to pilot error who either not monitoring their flight or just put random settings in the AP and leave it at that and then they panic when things go wrong.
I had this issue today when i was doing a flight from OMDB to Domodedovo… I was climbing with a V/S of 500 feet/min and following the SimBrief optimum flight level according to the weight. However; when i reached my cruising altitude; the aircraft started to bob up and down up to 300 feet/min. So I cancelled the flight 🤦♂️… This is not the first time I encountered this issue…
I can report that I am currently experiencing this issue with the 777-300er flying VHHH -> LIMC. My AP is set to an altitude of 36000 ft at Mach 0.84 with 46% load. I am following SimBrief’s step climbs, so I am quite certain this is not too high for the load. I was also at 30000 ft at the beginning and this was happening, if my current altitude is too high. The aircraft is bobbing with a vertical speed of up to 9000 ft in either direction, although it is only reaching a altitude variation of 38 ft in either direction. For any of you who think it is pilot error with a vertical speed too high, the aircraft climbs/descends at 100 fpm, as I use IF Assistant to step climb. So the altitude bug with the AP on the 777-300er is still there.