Try ammonia in a garden sprayer. Protect the floors and wear a respirator.Crack a window too. Ammonia will break down a lot of things that nothing else would touch.
Casey

Sand it and or scrape it off( paste or adhesive) with a wall paper razor scraper. Or just skim over it.

Here's a crazy suggestion, but it might work.

It sounds almost like what you're dealing with is rubber cement or one of its kin (who knows what great ideas pop into the mind of DIYers). If so, you should be able to buy a rubber-cement pick-up at at art store. This is a small square of gummy rubber that grabs rubber cement and lifts it off surfaces. It works on some contact cements, too. You should be able to rub it over the walls and remove the adhesive.

In defense of DIYer's I doubt that's what it was. My 1937 center hall colonial's center hall was done with this type of paste and they were NOT DIYer's. I don't have any suggestions since I picked mine off piece by tiny piece. You have my thoughts and good luck. It's a nightmare but worth it in the end.

TSP is really pretty amazing stuff. Yes, I know it's toxic to fish, but so are many other things we do. I dispose of mine by pouring it into the yard, rather than direct to wastewater. I use it as rarely as possible, but sometimes only it will do.

Sizing, I've determined, is only dilute wallpaper paste, which TSP is very effective for. If the stuff you're finding is not water soluble, then it's maybe something that went over the sizing.

I also use "tincture of time" a lot. Spray water, let sit, scrape or wipe; spray water, let sit, scrape or wipe.

Finally, I have one odd solution for some things... I paint over them (usually with latex), and once the paint is dry but before it's fully cured, it's easy to scrape or cut a lumpy substrate away. I use this for old, very hard paint drips and edges, for example, which come away sometimes like butter once a new bit of paint is put over top. If this glue of yours is lumpy, it might work.

Karin L