snapd 2.49, now in beta, tidies up the gadget validation code for volume layouts and partitions’ roles to fix some bugs and to prepare for the upcoming support for multi-volume setups for UC20 (where we will at least support having a main system volume with the system-* roles plus auxiliary volumes with other boot- and device enablement-required partitions).
The new validation code allows each system-boot|seed|data|save role to appear at most once across all volumes. This shouldn’t affect reasonable working gadgets, but let us know if you encounter issues.