Is it normal for my old .scad files to render differently on the release candidate?

The slowdown with boolean-heavy models is pretty common in the newer builds. The renderer and the way differences get evaluated got reworked between your old stable and the RC, so a hollow ball with a pile of cylinder cutouts hits the new code path hard. I ran into something similar with a perforated enclosure, same file, and the render time ballooned. The geometry ussually comes out identical, it just takes longer to get there on some constructions. The yellow console warnings fit with that too, they tightened up how it flags ambiguous intersections and stuff that used to slip through silently. Annoying, but it's telling you about things the old version ignored.

I keep both installed side by side and only fire up the release candidate when I want to poke at something new, since my printing workflow has zero tolerance for a render that hangs. One thing I'd suggest before writing it off entirely, if you do decide to report it, is trimming the file down to just two or three of those cutouts and timing that. If the slowdown scales with how many features are stacked in the difference, that detail in the report makes it much easier for whoever looks at it to pin down, versus a model with dozens of them where nothing stands out.

I've been playing with the new one too and noticed somthing similar but on a smaller scale. I made a simple box with a few holes and it rendered fine, so maybe the wait only gets bad once you stack up a lot of those cut-outs like in my big project. The yellow messages kind of spooked me though since I have no idea if they mean my print will come out wrong or if they're just being picky. Is it safe to ignore them if the finished shape looks right?