Steam won't sync my save, and my friend says to ignore the warning. Is waiting overcautious?

The play button brought up a Steam Cloud warning instead of my game. My friend said, "Mine does that sometimes. Just click through." We were supposed to start a co-op evening, but the same game also contains a solo campaign I've spent forty hours on.

I don't know which files the game keeps separately, and I haven't checked its backup instructions. I can see the warning; I can't see evidence that my save is safely stored somewhere else. I'm still using the same computer, so my friend thinks there is nothing to lose.

[Steam's Cloud guidance says an inability-to-sync error should be addressed before launching, and that ignoring it can risk conflicting files or lost progress](https://help.steampowered.com/en/faqs/view/68d2-35ab-09a9-7678). That is enough to make me pause rather than use his experience as a guarantee.

How do I handle the evening while I check the game-specific save information? I don't want to spend an hour guessing at fixes with somebody waiting in voice chat, and I don't want a friendship favor to become the reason I risk the solo campaign.