After upgrading to Resmed 11 I have had awful sleep for the last 4 nights

That helps a lot. One issue I see, but unrelated to your problem, is that OSCAR is reporting that you are in fixed pressure CPAP mode on the A11, but the graphs clearly show it is in Auto APAP mode. Must be a bug in OSCAR. I still use Sleepyhead. I believe OSCAR is supposed to be compatible with A11, but it appears is is not fully...

What I see unusual in the A11 graph of the mask pressure is that there are times when the mask pressure drops very low, below the minimum pressure of 4 cm that it is supposed to always maintain. See the screenshot below where I have highlighted the areas. It may be worthwhile to expand out some of those areas and see what may be happening first. It's possible that it is a chicken and egg situation. Are the deep breaths causing the mask pressure drop, or is the mask pressure drop causing the deep breaths?? You might see that if the time scale is expanded out in one of these. The one at 1:37 seems to be the worst.

These machines are designed to always maintain a minimum of 4 cm of pressure. It is possible that this particular machine is defective and cannot respond quickly enough to dropping pressure. Depending on where you got the machine it may be hard to convince them of that possibility. They may respond to a screenshot clip showing in detail what is happening.

One other thought I had was that you may want to try setting the machine to a fixed CPAP pressure to see what happens. That may let the machine respond better to quick deep breaths. Not sure, but it is easy to try. I would suggest a fixed pressure of 8 cm based on your data that you posted. Then it may have to be fine tuned up or down to get an acceptable number of OA events. But, 8 cm should be close. This is a bit of a work around to the underlying issue though if the machine is defective and not responding quickly enough.

You don't seem to be using the Ramp feature. If you want to try it, I would suggest setting the Ramp Time to Auto, and the Ramp Start pressure to 7 cm if you want to go with a fixed CPAP mode of 8 cm. That should be comfortable to go to sleep. The Auto ramp feature hold the pressure at the ramp start pressure until it decides you are asleep and then ramps it up to the set pressure of 8.

Hope that helps some. I would be interested in seeing a screenshot of that event at 1:37. It may tell what is happening first.

From what I can see on the one you zoomed in further it appears the mask pressure drop happened on a reasonably normal increase in flow. I am thinking there may be an issue with the machine's response to increasing flow and maintaining pressure. If you post more screenshots it is helpful to put the cursor on the event of interest and that should draw a vertical green line that goes from graph to graph so you can relate correlate each graph more easily. This is much easier for you to do as you can move the cursor back and forth sideways to compare multiple different events.

The event near the left of the top image at 1:37:30 would be interesting zoom in on. It appears to have multiple drops in pressure while the flow rate is reasonably normal. But the exhale (down) flow rate seems to have a lot of noise on it. One possibility is that the flow rate sensor is not measuring flow reliably and that in turn is affecting pressure.

You could also search the S9 graphs to see if there is anything similar in them. If not, that would seem to eliminate you and the way you are breathing as a source of the disturbance.

Just of interest that squiggly line in the middle of the bottom graph is the machine pulsing the flow to test for the type of apnea you are having. If it is obstructive the cycle up and down in pressure is more extreme. And if it is an clear airway or central event then the wave in the pressure line will be narrower. This event did not last 10 seconds so it was not flagged. the next event lasted longer and did get flagged as an OA event.

On further point. When you move the green vertical cursor line left and right on the screen with the mouse you can read the exact value of the variable in the top left of the graph. This is useful for seeing how low the mask pressure is going during these events.

I am not aware of being able to troubleshoot the problem any more than you have done. I think I would talk to your supplier and try and get them to accept a return and replacement of the machine with a new one. Your screenshots should be useful in verifying that the pressure is not being held constant, and in fact is dropping for no reason. I am just guessing but the machine pressure control system may be programmed to use flow as an anticipatory input to determine when to increase the fan speed. When flow goes up the pressure will tend to drop if the fan speed does not increase. Possibly a defective flow transmitter would contribute to the pressure dips.

You also have your S9 data to show that it is not your health problem and the S9 works well when the A11 does not. My wife has a S9 machine which has been displaying the motor life exceeded warning for about a year now, but it keeps on ticking. That is good because the on line supplier of machines in Canada seem to have no stock of new machines.