The code to blend multiple Light Probes is broken in 3.8 and smooth blending no longer works:

It looks like this code was refactored to use jme's #for preprocessor, and the probe blending must've gotten broken in the process:

https://github.com/jMonkeyEngine/jmonkeyengine/blob/master/jme3-core/src/main/resources/Common/ShaderLib/module/pbrlighting/PBRLightingUtils.glsllib#L590

I haven't worked with this specific probe lighting function before and currently I'm burnt out on shader dev and moving on to other things, so I don't plan to dive into learning more lighting code right now.

So I plan to just revert the code in the probe lighting function to its pre 3.8 state, since that's the quickest solution and does not require me debugging any new code.

Unless @riccardobl if you want to take a look and get the current code working, then I can wait and hold off on reverting the probe lighting code.