Just looked on the Roon site and this issue in one way or another has come up a few times, it seems to have something to do with Multicasting, don't ask me to explain ... please.

Anyway one solution seems to be to check the box in the Orbi app 'disable IGMP proxying' somehow this interferes with recognition of Roon/Sooloos endpoints when using the Orbi router and satellites setup.

Hopes this works, Gerard.

Home Theater: LG 4K C7, HD621, G61RSL, Oppo 203, MS600, DSP3100 L & R, 2x3100's centers and 4xDSP3100's surrounds. 2x REL S3 SHO and 2x REL habitat1 subwoofers.
Music & TV: Sony 4k XBR 65", Oppo 203, HD621, G68D, C15, 588, M10, M20's, M33's, 4xDSP33's
MD600, 2xTwinStores.. 2xMS600, F80, Prime headphone and PSU.