FWIW, I tried the above test again late last night before sleeping. Checking this morning, I see that all the photos/video from the phone sync’ed successfully overnight.
What would be good to know is if there is a default time delay that it takes for photos or anything else to sync? It seems notes and contacts are sync’d fairly quickly.
I did a bit of debugging with e-0.12. Per sync config in /e/ there’s an interval of 30min of syncing content and this one was crashing. That said, a charging or boot event will trigger another type of “intent” (no Android dev, sorry for terminology) and a sync will complete successfully in my observation. As I’m now on e-0.14 I’ll have another look soon. Charging was my workaround.