Seems after v138 there is issue if in the same network Shairport is runnng on several RPIs. Until v137 I didn’t observe this strange behavior.
I have in the same network three Raspberry PIs with the Shairport installed.
When each of RPIs is booted separate and alone, then AirPlay nicely see each of them and play.
When several RPIs are booted concurrently, then only the first who started is visible, the rest are not available.
I have given individual names in Shairport confit on each of Raspberry PIs, but it somehow feels that all of them are registering with some similar number, and therefore there is conflict.