BUBBLES.......

Something bubbling is moisture, and same with peeling.

Your surface was not completely dry, primer was not thoroughly dry and cured.

Either way, get it all off and start over.

you need a high adheasive primer like KILZ

The Valspar and Kilz are both bonding primers.

Bubbling.is almost always trapped moisture.

Get a heat gun and scrape all that mess off and start over with a better sanding, then a better quality primer, BIN shellac based primer.

You painted to sson the primer was not the right one IMO either . I use Kilz usually or a shellac based one since it is always a mystery what was done before . BTW vinegar does not clesn this actually you need to use something to cut through years of greasy hands ans dust and god knows how many different wood polishes . I do agree now take it all off makes sure the part you want to paint is as clase as possble to be down to bare wood then the primer and leave it for as ong as the can tells you and to be safe longer it takes time to cure and IMO you do not paint until that time is up for sure.

"Did you use latex paint over oil paint?"

Latex over oil is perfectly fine, it is the other way that does not work.

I think I would have stripped the mantle to bare wood before priming/painting. The original glossy finish isn't going to take new paint well.