Jar pasta sauce resealed itself in fridge overnight. Is it safe to eat? I opened a jar of heavy cream pasta sauce (pumpkin, tomato, cream, etc), ate some and stored the rest in the fridge. The next day it seamed to have sealed itself. The button stayed down when I happened to press it. When I opened it the second time it popped loud. Like new.

Why did this happen? Is it safe to eat? The sauce was store bought. Thank you.:)



Additional info added by OP (in a now-deleted answer):

I put it into the fridge within 20 minutes. But it was room temperature when it went in the fridge. I didn’t heat it at all and it wasn’t especially hot weather.

I asked because sealing seems significant. And it resealed itself with no action on my part. Should I check my refrigerator? Could a jar reseal on its own happen if the fridge temp was unstable? (The power didn’t go out but it's possible it could have been finicky in the storm overnight.)
If you put hot (or even warm) sauce in a jar, seal it, and place the jar into the fridge, as it cools, it (as well as the air in the jar) will contract. The larger the temperature change, the greater the vacuum that will be created. 

Most likely, what you are seeing is warm sauce cooling and creating enough vacuum to suck in that button on the lid. If that's the case, it's perfectly safe to eat.

You say you opened the sauce, used some, and placed the rest (immediately??) into the fridge. That's a perfectly safe procedure for saving leftovers, so long as handling of the sauce did not introduce cross-contamination (ex via "double dipping").