Not sure, but try shortening the release?
Sometimes, long note releases can confuse true legato settings.
ie. the release tail engages legato for the 2nd note (if notes slightly overlap), which is fine, but for 2 notes of same key, the 2nd note may be muted. Either shorten the first note if in an editor. Or if playing, manually shorten the release time setting so that fast triggering doesn’t cause tails to run into the successive note.