As there were a few topic that seem to be related we decided to make one topic so we can try to understand what is causing this. Let's start with what we know.
We have 21 people on file that reported this (that far below one promille of users)
3 have not replied to our attempts to get more info
9 have reported their issue solved
2 by using correct procedure
1 by making sure FPS was high enough
6 by re-installing the sim.
Leaving 10 users who still face this (likely there are some more that have not been in contact with us
We are unable to recreate this reliable on our systems (other then my making deliberate mistakes in speed management)
We know our code has some loose ends that might make the path following a bit sloppy (but not in the degree described), it seems unlikely this is involved in these cases.
Because the issue only seems to affect a certain group of users the difficult task will be to identify what makes these user unique among the total amount of customers. There has to be a local element to this problem. Something that triggers it for these customers.
The first thing that we can think of is an incorrect simulator after updating from a previous version. In another issue we have seen this over 70 times and reliably fixed by fixing the sim. It did not work on an updated sim and it did work on a cleany installed sim. That this affects only this aircraft and not others is simple to explain, we are using the June 2018 compilers from Lockheed that absolutely needed the latest version of all files. These new compilers are a big part in what makes this aircraft so light on FPS so we don't even consider going back (and it would cause more issues with bugs that Lockheed fixed). As said we seen another far more common issue (the st elmo's fire bug) that is reliably fixed by a correct clean install of the sim. That proofs the updated files where not correct.
Next to the sim files option, the second most likely cause is frame rate. It all can be explained when framerates drop below our 16 fps threshold, even for a short moment. When the FBW system gets upset by that it can start to hunt itself. This was the case for the single user reported above. He had the issue consistently and had relative good fps, but when he increased the FPS the issue was avoided. Most likely short low fps moments caused the issue.
The next possible reason is user error. Speed management is not the easiest thing in an Airbus and often overlooked as a factor for problems. Also abnormal loading could cause issues. For two users this was most likely the issue. One had incorrect settings in MCDU, the other did something else wrong that we still do not understand,
A possible cause is jittery controllers, we seen that a few times in other products and would explain why this happens to so few users.
The last cause could be weather. Some weather tools insert rather violent changes in wind patterns (and often very thin layers and very small 'blocks' of weather. our busses have always been rather sensitive to this. Strong changes in IAS cause strong changes by the FADEC and when the aircraft hits another layer before things have smoothed out the aircraft systems can get overloaded. It should happen far less than with previous releases but still a good possibility.
At this moment we do not have any changes that could affect this behavior planned for the simple reason we do not know what to change. The loose ends in the code will be fixed with SP1 but as said we do not think they are related to what these users see. They will only smooth out the movements and make it stick a bit better to the profile.
The users who still have these issues could do us a huge favor and fly the step-by-step flight (following all steps), with zero weather and very low scenery settings. If that solves it for some we are one step closer to understanding what is happening. This flight has been flown by us hundreds of times so it is the best benchmark. If you do see problems please let us know EXACTLY at what step.
in the end I am sure we can solve the issue for most users, but as always there will be some occasions that we'll never understand. We have had that with every product. In those cases only a complete format of the disks is the solution. Far from ideal, I agree, but it would mean you have a 99.99% chance of being one of the tens of thousands of users who don't have the issue.
I do thank you all for being patient and cooperative. We absolutely understand it can be frustrating, also for us. We want you to enjoy the product after all.