I had the same issue after last general Ubuntu update. My scree resolution switched back to generic/standard (rather than my selected screen resolution for the monitor which was much higher). The system said it was using 535 but like you, I also when investigating the error log the Nvidia driver was not loaded and the system could not communicate with Nvidia driver.
Clicking on the Nvidia app in the panel also informed me it was not running.
My solution (before switching to full CLI reloads of the Nvidia driver) worked and was as follows:
(I of course could still see my screen)
I used the GUI for 'Additional Drivers' (tab) in the Software Settings app to reset my driver.
(1)I first reset it to the standard Nouveau driver and then reboot.
(2) I then checked the Nouveau driver was selected in Software Settings - additional Driver
(3) I then selected the original Nvidia 535 driver (that I had been running) got it to reload and everything seemed fine once again.
(4) I rebooted the machine just to be sure and since then things are back to normal.
I think this process "under the hood" reran the install of the driver and adjusted any settings/headers etc. to their correct value.
This worked for me. But everyone else may have a different experience.
