I have the following mods installed:

And these following resource packs:

When there are cascades, I don't get the ambient sounds that I would have got in previous versions. Is this intentional? Or do I have a conflict somewhere?

Have you checked the config? You might have changed the option in the past and forgot about it

Same for me. Just effective + quilted fab api, default config. Anything after effective 1.3 doesn't give the cascade sound. I've just been sitting on 1.3 because of that.

Like I can take the exact same minecraft instance, same configs, drop in 1.4 or 1.5 and it stops working... put back 1.3 and it works again.

Guess I should mention this is: 1.19.2, quilt 0.17.6, qfapi-4.0.0-beta.17_qsl-3.0.0-beta.19_fapi-0.64.0_mc-1.19.2

Same for me. I disabled all mods but Effective and Quilted Fabric API. No sound, config is default, no RPs.

1.4.1 added a mechanic that makes waterfalls not play sound when not visible, to avoid underground waterfall being heard above surface, but if it removes all waterfall sounds because one block is blocking the view, I'll remove it