Strange ADAT issue

I have two MR816CSX’s connected via ADAT to an RME UFX.

Everything appears to work fine, but the ADAT light on one of the MRs does not light up and the corresponding ADAT light on the RME flashes intermittently.

Looking at the RME UFX USB Settings, Input section, it flashes Sync or Lock as the light on the front panel flashes - However - if I connect Firewire cables from the PC to one of the MRs and then daisy-chain on to the second MR the RME indicates perfect Sync and the front panel ADAT light remains constant - But the ADAT light on the MR still does not light up!

BTW, I know that the Firewire connections are not necessary with my setup as the RME is connected via USB and the MRs via ADAT - I just connected them initially so that I could change the sample rate on the MRs.

Confused - me too!

I’ve checked all the settings on the Yamaha Steinberg FW Driver screen and the MR Editor (both MRs are set to ADAT) and also swapped out the ADAT cables.

As I say, the system seems to be working fine and I can not be sure whether or not this is a new situation, but something is probably not quite right here.

Any ideas?