DisplayLink displays runs at 1FPS when laptop lid is closed.
In recent Ubuntu 20.04 users started to report extremely slow refresh rate on DisplayLink screens run by udl or evdi kernel drivers. This issue is happening only when external DisplayLink display is the only one which is enabled. Opening laptop lid or enabling laptop main display is resolving that issue.
Together with help of our end users we have found that this issue started to happen in X.Org X Server 1.20.6