The volume cannot be increased past 15 in one of my rooms that has its own amp and uses ceiling speakers. When I try to increase the volume it automatically adjusts itself down.
To avoid confusion, I have no arc or TV in room, not is any other amp in my house tied to this room. It is a standalone amp.
It sounds like you have a volume limit set.
https://support.sonos.com/en-us/article/setting-a-volume-limit-on-sonos-products
As a test, disconnect the speakers, then attempt to adjust the Volume. If this is successful I suspect that there is a wiring issue and AMP is simply protecting itself.
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