SB2 base model intermittently "forgets" about the battery in the keyboard base

I've been having an odd issue with a Surface Book 2 13.5" (Core i5/8GB/256GB) we use for lab testing. During use, it will sometimes forget that it has a battery in the keyboard base and the remaining battery life will suddenly jump from ~8hrs to ~2hrs.

There is no interruption in keyboard/trackpad/USB device connectivity or docking port functionality, but this is sometimes accompanied by the green attach/detach popups.

I have thoroughly cleaned the tablet->keyboard connectors assuming that the issue was there. Also updated all firmware, uninstalled/re-installed drivers etc, booted to BIOS, etc.

If I shut down the system, the battery re-appears OK and will charge just fine.

Anybody with a similar symptom?