If you run Victron Multiplus in series with a Phoenix or another Multiplus (I know, not supported, but has some benefits over parallel) - VRM double accounts the power data. Anything generated by the Upstream inverter is accounted, and then accounted again as Input for the Downstream inverter.
You can of course disconnect the VE.Bus MK3 USB input from the upstream, but then you lose control as an input.
A single “Flag” in VRM saying “Do Not Account” for this device would largely solve it. It’s similar to the lack of DC accounting, but in reverse.
Ideally would be support for Series - but that may be stretching too far.