Good to know.
I had the exact same problem with my Apple TV 4K (along with different problems with the app on my Roku 3) and contacted Criterion's tech support. Here was their reply:
"I sincerely apologize for the delay in getting back to you and the problems you have been experiencing. We are currently experiencing a high volume of support requests and are working as quickly as possible to get these answered. We appreciate you reaching out about the problems you are encountering and providing that helpful information. I can confim that both problems you have mentioned are actually ongoing issues with both platforms that our engineers are investigating and hope to have a fix for soon."
For the record, I had the exact same problem last fall when I first got Filmstruck. It eventually cleared up. I presume Criterion will figure it out soon as well.