Issue with Vsync keep going back to default

Hi

I have a question regarding Vsync. It seems that recently, my sim is going back to default (No Vsync - aiming for 60fps which is my native resolution hz) however I have always set Vsync in Nvidia control panel and then in MSFS at half refresh rate so that my FPS are locked at 30fps and it has always been silky smooth for me.

I presumed this was due to the graphics driver that I installed, so I uninstalled that, and reinstalled the latest then set Vsync in NVCP and MSFS.

I start the sim, and it locks it at 30fps perfectly, but for some reason after a few minutes, it shoots back up to 60fps.

Is there any logical reason it could be doing this?

Many thanks