Both and/or neither and/or user.

That's the benefit of dedicated Sooloos hardware. A lockstep environment that minimises incompatibilities between versions, unlike third party kit that will always be a moving goalpost.

If Meridian said to upgrade and/or said that version was compatible and it isn't, then they should issue a fix, otherwise QNAP should try and maintain backward compatibility but sometimes it is unavoidable that incompatibilities may creep in.

One has to ask why user upgrades, especially iirc that Meridian recommend using NAS dedicated for Sooloos. If that is so, then its the users responsibility.

Imho.

Meridian owner since 1992
Prime & PSU, Focal Elear headphones, Roon (ROCK 8Gi5 NUC), Explorer 1 & 2, F80. 200/203, various Sonos (via Roon).