Sorry for the delay. It actually took a little bit of effort to figure this out…
I’m using a slightly different (and lower-level XPath…) nodeset filter here, but one that works as desired for both Enketo and Collect. It basically performs the equivalent of the previous indexed-repeat() [but works for both! 
].
Enketo and Collect use different XPath engines, so (rarely) nuances in their different behavior surface, particularly when dealing with uncommon/esoteric stuff like filtering between repeat groups and select-from-repeats…
select-one-from-repeatsV2.xlsx (10.3 KB)
Tested against Enketo
And KoboCollect
