In the 55 countries I've been to, I can't recall ever seeing them stamp a page and then put a sticker on. I'd think it more likely something that was built into the sticker, that left the residue.

I have some visas that start to peel off on their own. El Salvador is the worst one. Indonesia had some that the printing seems to have mostly rubbed off. I think they bought some dodgy printer cartridges.