I would try the shader cache suggestion.

 I had the seemingly same issue yesterday without making any changes recently and I did the shader cache cleaning after the recent windows update and all is back to normal. Hope it works in your case.

 

I had a problem like that, and it turned out that Nvidia settings had somehow changed back to integrated graphics.

4 hours ago, Alvega said:

Check that you have vsync disabled, both in sim and Nvidia control panel, to make sure nothing is locking your FPS.

I'll check the sim tomorrow, but a quick check in the nVidia CP shows Vertical Sync set to On.  Instead of turning this off, which may lead to tearing, would it be advisable to change it to Fast?

Edited October 27, 20232 yr by RandallR

2 minutes ago, RandallR said:

I'll check the sim tomorrow, but a quick check in the nVidia CP shows Vertical Sync set to On.  Instead of turning this off, which may lead to tearing, would it be advisable to change it to Fast?

Nope. If your monitor is 60Hz and you have 33% refresh rate set inside the sim you have it locked to 20FPS and that's probably what's causing your problem. So disable it just temporarily just to see if your FPS come up or check if you have 33% refresh rate set inside the sim.

 Delete the rolling cache 

3 hours ago, Alvega said:

Nope. If your monitor is 60Hz and you have 33% refresh rate set inside the sim you have it locked to 20FPS and that's probably what's causing your problem. So disable it just temporarily just to see if your FPS come up or check if you have 33% refresh rate set inside the sim.

All V-sync is now off - there was no limit on the refresh rate.  The rolling cache has been reset for the 2nd time and the shader cache has also been deleted and reset to the new recommended parameters.  I'll find out in the morning if this makes any difference.

Somewhat a wild guess here, but I recently had a very similar "overnight" significant drop in FPS, especially in high density areas.  Three things fixed it for me, two which you've already done, which are to delete and rebuild the MSFS rolling cache and clear all nvidia driver caches.  The third was to quit using DX12 and go back to DX11, for DX12 now uses nearly 50% more of your gcard's vram than DX11.   FPS is seriously lowered when the gcard's vram space is depleted; there is no warning when this happens other than a dramatic performance drop.  Hope this helps.

Edit: whenever you switch between DX versions in MSFS, clear the nvidia caches before restarting MSFS.

Edited October 28, 20232 yr by TheFamilyMan

Try reflex low latency mode

OK - here's an update.  After doing all of the following:

• Deleted/recreated rolling cache
• Deleted/reconfigured shader cache data
• Turned off Vsync (both in-sim and nVidia)
• Set Reflex Low Latency

Performance was slightly improved, but still not at previous levels.  I was able to complete a flight again.  I'm still unable to achieve a constant 30 fps as I was before.

Both while sitting on the ground prior to takeoff and in cruise (heavy live weather and in a metropolitan area for takeoff - cruise over farm terrain/moderate weather at FL300).

• FPS: 20-30 (about 22 average on ground - 27 average in cruise)
• CPU: 31-95%
• GPU: 24-40%
• VRAM: 72%
• RAM: 57%

It appears to me that I have a CPU issue? The waveform looked like someone on a heart monitor having continuing anxiety attacks!  See below.

On ground at the left - cruise on the right.  I'm going to pick up some fresh thermal paste and hope that brings her around.

there are many tools to check your CPU & GPU temperature (TechPowerUP GPU-Z). A very popular CPU & graphics benchmark is 

https://www.maxon.net/en/cinebench

that would show if your CPU is throttling down.

Thanks - I have NZXT Cam.  When NOT running FS everything is fine - I'll run a test with the sim running later today.  I hope to be applying new thermal paste on Monday and we'll see if that makes a difference.

Here is an excellent tool for monitoring all aspects of CPU performance, it'll reveals all you need to know if your system is thermal throttling.  Good lucky in your endeavors.

https://www.hwinfo.com/download/

BTW, I've been using this tools for years.

Well - quite a change today.  I will still be replacing my thermal paste in the next couple of days, but a flight today showed improved and (more normal) performance.  I did measure temps and both the CPU and GPU were in the mid-80's F range.

Performance was good (and smooth) - the left data was prior to takeoff - the data on the right was at cruise.  The weather was clearer today and I was over Italian terrain instead of cities and farmland.  I'm glad that I'm doing this work, but the performance last week was so poor that I'm thinking it may have been MS server issues more than my system.

You are still hugely CPU limited with such a low GPU usage. I would invest this GPU overhead in better image quality (by increasing render scale for example) as it is a known fact that if you move more load over to the GPU and reduce CPU limitation, you sim will run smoother. 

If the SIM runs fine and all of a sudden Performance is getting worse, without any changes made, i wouldn't change anything on my side. After 2 years of MSFS my conclousion is that the bottlenek in most cases are found in the streaming part.