You can't change the UUID because both devices are still part of the same pool, do this:
Stop the array, if Docker/VM services are using the cache pool disable them, unassign all pool devices (from both pools), start array to make Unraid "forget" current pool config, stop array, reassign both devices to the same pool (there can't be an "All existing data on this device will be OVERWRITTEN when array is Started" warning for any pool device), start array, pool should mount normally and you can start docker/VM services if stopped before, now see here to remove one of the devices from the pool, when it's done you can re-add it to a different pool (it will need to be formatted).