My ISO and shutter went back to the default after screen went to sleep

I saved some settings to the C1, C2 options on the dial of my 5dm3 earlier and I think I was in C2 and I needed to boost the ISO and change my shutter a bit, and I stopped taking photos for a little bit and the screen of the camera went off and when I reactivated it all of my changes, reverted back to those of the C2 saved settings. Is there any way to stop it from doing this when shooting in one of the C modes?

Thanks.

In the 'Custom shooting mode (C1-C3)' menu, set 'Auto update set' to 'Enable'. That should fix it.

It's not a perfect solution because it then means that you lose the base settings that you initially entered in the custom shooting mode. To avoid that, you could instead disable 'auto power off' mode (Tools menu set) as part of the relevant custom mode base settings themselves, leaving auto-update disabled. That is going to burn a little juice but not a whole lot, I would imagine. This way, after you have powered down, the next time you use the relevant C1-3 setting it will have reverted back to your base custom setting again.

I do something in between. I set the timeout to four minutes in the Cx modes.
Why Canon can't implement a temporary update is beyond me. That is, let it update the settings during the session, but don't let these updates survive a power down or change to another mode. That would in one bold stroke eliminte 98% of all complaints about the custom modes.
It would also mean that if you just want to return to the baseline, simply switch out of the custom mode and immediately back in again, and you have your original stored setting back.