Perhaps a few more details might help. Sw version, current GPS settings, bike details, even a screen shot of the incorrect distance. Have you tried exporting the fit or GPX file and reading it in another application? Unless you are in something like ultra track mode the various other modes will not lose you 40%. Does the track look good?
Then it's highly likely that the configuration is not correct. Check on your watch under sensor settings if you find you E-Bike (potentially paired as speed sensor) and check the wheel size settings. If it is on "Auto", try setting it manually. If a value is configured, you could try to set it to "auto" or set the correct value manually. The correct value is the outer circumference of your wheel.
Whenever I see 40% I wonder if it is a km vs mile issue but, in this case. I’ll bet #Matthias has nailed it with an incorrect speed sensor connection. Assuming in Connect the track (route) looks good then GPS is fine but speed (distance) is coming from the bike sensor.
