My non-solar edge 840, 9.29, records an unusually high number of RR interval values of 5.000 seconds. These values occur when stopped and are interspersed with apparently valid values. In one case I had ~110 values of exactly 5.000 seconds in a one hour stop. In that case the record timestamps before and after the stop jump by 495 seconds more than the sum of the RR interval values while stopped, so 8.25 minutes of HRV data was not accounted for during that stop.
HRM is Garmin 010-12883-00 HRM-Dual Heart Rate Monitor.