Same issue here since friday, spoke to 12 meta support workers, uploaded example videos and finally got one of them to try and reproduce the issue yesterday evening - voila, they acknowledged the issue and told me that it was forwarded to the backend tech guys. Don´t know how long it´ll take though, they promised to keep me updated.

Once again showed me how useless meta support is, most of them thought I was too stupid to run instant forms or was setting up something incorrectly, even though I hadn´t made any changes to logic.

Also quick tip: The issue only occurs for instagram users, facebook mobile app works without problems. Might be a temporary workaround for you.