I heard of people having issues submitting Strava results for VNRRC. One individual attempted a number of times to do it following the instructions carefully and each time it appeared that it worked but his result never appeared.
Finally he submitted it removing the iframe details from the URL so that it started from the https: after the src= of the iframe and it worked straight away. Not sure if this was a one off or why for this individual it did not work including the iframe details which you discard anyway.
If it is a wider problem then maybe change the instructions to say to only include the bit that looks like https://www.strava.com/activities/3227772874/embed/023201472a28a6fad38a23bb7c142a92d503ddb4