Hi there Murman,
Our technical team has logged this issue / verifying or we have an bug in Isadora 3.1.1 on MacOS.
You seem to be correct that Isadora 3.0.8 (macOS) is fine. Windows on the other hand doesn't has any issues both on Isadora 3.0.8f12 and Isadora 3.1.1
Will keep you guys updated.
For now sadly I don't have a way to get the actor working with HTTP URLs on MacOS.