When the split occurs, my 210 will always display Blue and my 218 Green.
1. If your 210 is decoding the MQA, then the 218 should be showing magenta, because it's acting purely in a rendering capacity and is unable to authenticate. This is a cryptographic consequence of doing the first decode somewhere other than the device that is rendering. (And the 218 is rendering even if you use the digital outputs to DSP loudspeakers).
2. If your 218 is *not* decoding the MQA, then this feels an awful lot like the 24-bit MQA stream being stripped to 16-bits (which will still be recognized as MQA, but green MQA).
In case 1 there would appear to be a bug in the 218 in that it's showing green instead of magenta (although there is the possibility that it *can't* show magenta).
In case 2 there would appear to be a passthrough bug.
Are both devices running the very latest firmware? The 218 in particular received rendering fixes a while back.