Normalised Power value displayed as Average Force

noticed that rides recorded on my garmin 840 when viewed in the activity history on my fenix 7 display average force instead of  normalised power . normalised  power shows either zero or a few thousand !! when I view the ride stats in the 840 or garmin Connect all looks ok i.e. normalised power has a correct value . this has only just started happening recently.  anyone else experience this