Elevation gain Tacx app vs Garmin not same

Hi, I have noticed that there are differences in elevation gain between what tacx app says and what is in the end (after finishing workout) in Garmin Connect.

Example: yesterday I did ride within Ride with the Pros 2024 Challenge, the course name is Team Lotto-Dstny - Vall de la Gallinera and it says 44,3 km and 819m of elevation.

In Garmin Connect I see 44,3 km but elevation gain is 1267m which is more than 400m difference.

Another ride: Saint Moritz - Lakeside Mountain Bike - 103m in Tacx, 107m in Garmin

Is this known issue or not? I havent been using Tacx as of March this year but dont remember such differences from last year rides.

Thank you.