I think it’s simply different powermeters report different power, even if calibrated. Why not use you powermeter for both garmin and Xert?
The other thing, probably second order, is that if you have the activity twice, your signature changes a bit from activity to activity (due to strain and any BT) so numbers will be a bit different (shouldn’t be huge though)
I had this case before and it’s just that my fitness signature was updated between the first and second activity so the second activity (it was the same as the first) looks different as it was placed after a breakthrough
Actually a SMART workout performed as a group session would be more effective but that’s another story.
@hugoyave’s answer sounds likely with a pre-adjustment chart shown in image #1 and image #2 with the updated signature applied.
Image #2 is still “fake news” though. You have to disable power smoothing in the Wahoo app to resolve that.