Intervals.icu now sets “thresholdOverride” in the data uploaded to the Zwift API to your Intervals.icu threshold pace.
It seems you need to fill in your 5k time on your Zwift profile using your Intervals.icu threshold pace to calculate the time.
In these screenshots my threshold pace is set to 5 mins/km. So I have captured 25m for my 5k time:
And the workout seems to be ok:
