The June 24th Steam Update (version 1782257239) changed stuff that impacts Cloud Saves. I have not had the energy to fully tear it apart and cleanly solve the issue in a way that makes me happy (burnout) but I needed to get a fix out, so I sent a good chunk of my evening tearing apart this update, trying to figure out this intermittent/inconsistent crasher. Chasing a ghost. I found the responsible part and engineered a temporary hack that restores functionality. Data syncs, no crashers, all good.
In the near future, I'll fix this correctly and neatly. For tonight, this is good enough.