Thanks for looking into it.
Below is the result resuming from a sleep and 2 hibernations with power management enabled. Problem appears resolved and only one error event is output:
However for another Dell owner with Windows 8.1 power management was already enabled and removing Intel Rapid Start Technology solved it (not even installed on my Win 7 machine).
Seems there is no single cause or solution, simply that the driver is very flakey in reconnecting. Clearly if these solutions worked for us it must be the driver conflicting with Windows and/or Intel's own bloatware.
It's a shame Windows has matured into a safe/reliable OS but hardware vendors ruin it by layering a ton of buggy, proprietary stuff on top. I have 10 factory-installed Intel apps installed and no idea what half of them even do.