Haven't had the time yet, but it's on my to-do list. Just not sure if they will support this as I'm running it on my own hardware, not their laptop.

Does the system also freeze on lock screen without the sleep? superkey(winkey)+L

No, lock screen works fine.

Cheers for the links, I'll look into that!

I was able to make some progress in troubleshooting.

I went to the Screen Locking options and disabled "Lock after waking from sleep". Now I get to see the screen when I wake the computer back up, frozen as it was when I issued the sleep command.

All devices are disconnected - no network, no Bluetooth, no audio, all the “tray” icons are greyed out and/or showing errors, time is stopped at the moment I clicked the "Sleep" button.

Not sure if that helps at all.

Would this part potentially get in the way of the method you suggested?

One fairly recent thread had a proposed solution of adding "mem_sleep_default=deep" to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub.

Should I remove that?

I moved to Tuxedo from Kubuntu after having MASSIVE problems there, but I honestly can't remember if I was using the Sleep feature.