"disk not ejected properly” when on Firewire 800 port


My G-drive, 1TB Gen4 99300-13103-001 is working fine on USB 2 on my MacMini late 2009.
When using it on a Firewire 400 it works fine too as a backup drive for Time Machine.
Any time I try to use it on either Firewire 800 port of it on my MacMini ig gives me after a while this message: “disk not ejected properly”.

I have about tried everything possible but there might be something I missed out. Is it possible to reduce baud-rate on MacMini FW800 port to 400 and how or is there another solution?

I Tried the SMC resets, etc.