Welcome to the Roku Community, @CrankyB!
Thanks for letting us know about this here. We'd like to provide further information about the playback issues you've experienced within the Acorn TV app.
Please be aware that most standalone apps on the Roku streaming platform are managed and maintained independently by the channel provider. We're glad to hear you've already coordinated this with their Support team, as they will be the ones who can fix this error on their app.
We hope this will be sorted out soon.
Best regards,
Carly
Carly Y.
Roku Community Moderator