LoBase layer of paint resists chemical stripping
It is likely milk-based paint, which often resists remover.  Unlike normal paints that just need a solvent to remove, milk paints require a caustic, such as lye.
Oddly enough, it sounds like PeelAway 1 could work to remove it, but another option would be Real Milk Paint remover.  It is essentially lye with some added stuff to make it a bit easier to handle.
I haven't used it myself, but as the entire basis of the company is milk paint, it should be good.