I noticed that since FW 12.20 it is no more possible to import EDGE 520 fit file with R-R values in Firstbeat Athlete software : there is an "Invalid R-R format" message while import attempt.
The changes are minor because I don't see any difference when using Fit File Tool Repair to analyse the 12.20 Fit files : R-R values are there.
Something related to Fit format evolution or CIQ 2.3.3 implementation?