Wrond activities duration in Zwift

Dear community,
I am quite new on Zwift. I bought my first Home Trainer and subscribed to Zwift a couple of days ago
I did 3 trainings and I have a problem with the duration of the activities registered in Zwift
I did a 1h07 training registered as 37 min in Zwift (while I did run 1h07 without interruption and with the Zwift application sending the “right power instruction” to the home trainer)
Same yesterday, I did the 30 min Emily Shortmix and the activity registered in Zwift is only 18 min long.
Did anybody faced the same issue ?
Many thanks in advance and best for 2K21