The other day, I noticed that my phone was very warm and the battery was going down fast. A quick look at htop showed it was Google Photos. /system/bin/logd also has high usage when Photos is busy. The combined load spikes three of the CPU cores to nearly 100%.
This activity seems to happen regardless of whether there are photos to back up, and it continues even when Photos is in the background (swiping the app away from the Recent Apps list, however, is enough to stop it). Backing up photos doesn't seem to work properly either, as the app claims I have 105 to back up even after being left open to do so overnight. I've even tried removing all pictures from the folders to be backed up, and it has yet to update that status.
I have tried clearing all of Photos' app data (twice!) and all cache data for apps (but not the /cache partition, at least not yet), to no avail.
Phone is a Droid Turbo (XT1254) running Android 5.1.1 (stock firmware). Photos version is the latest available to me (Photos 184.108.40.206833446).
Has anyone else experienced this issue? Are there any known solutions to fix the problem?