Hey , Garmin-Matthew,
please have a look a the following 2 activities recorded with the 530 and the 945:
https://connect.garmin.com/modern/activity/3982929563 - 530
https://connect.garmin.com/modern/activity/3982939599 - 945
The elevation profile on the 530 is way off, as the track is a return one and basically it should mirror itself after 52.5 km; the profile on the 945 is correct.
Put this on the bug stack please ;-)
Kind regards,
Tudor