Thanks Simon.
1.confirm that you're using the latest driver and firmware for the Fireface? - Yes (Version 3.125).
2.change the sample rate and buffer for the Fireface - use 44,100hz and set the buffer relatively high. - 512 and 44,100hz.
3. Firewire chipsets - the Texas Instruments.

Not sure, but I have a feeling that maybe it has something to do with the "Plugin" changing between 2020 and 2021.
Just a gut-feeling.