Are petroleum-based products prone to produce hard residues with black powder?
The answer may be more simple than some may expect, I start with Black powder, which contains, to quote:

Black powder is a granular mixture of

a nitrate, typically potassium nitrate (KNO3), which supplies oxygen for the reaction;

charcoal, which provides carbon and other fuel for the reaction, simplified as carbon (C);

sulfur (S), which, while also serving as a fuel, lowers the temperature required to ignite the mixture, thereby increasing the rate of combustion.



Next, the warming of an organic together with sulfur can produce a volatile sulfur-containing compound (see, for example, 'Reactions of sulfur with organic compounds XXI. The action of sulfur on 2-thienylchloromethane and di-2-thenyl sulfide').
Further, mixing of the new compound with carbon powder could account for the observed product especially after evaporation of all volatiles.
Note, per the comment: &quot;problems of stinking, liquifying or decaying animal greases, and some people tell they used petroleum jelly or lithium grease for decades with no particular problems&quot;, the precise sulfur-based product, if any, created could account for the differences reported.
Also, this proposed explanation requires an element of heating, which likely accounts for the development of the reported problem over time.
So, to precisely answer the question: &quot;Are petroleum-based products prone to produce hard residues with black powder? Yes, per my assessment.