The equal power crossfade tool (pretty sure that’s what it’s called) is very useful. Probably my most-used tool of all. I think that’s the one danoise mentioned. Works flawlessly in 3.1 still.
Indeed, that was the name. Now I could find the link:
https://forum.renoise.com/t/new-tool-3-0-xfade-pow/41920
it’s easiest to stick with 0-crossings, as mentioned. This becomes much more difficult with stereo samples, of course.
If you encounter such an “impossible-to-loop” stereo sample, you could always split the sample into separate channels. I never did this myself, but at least it’s possible 