The Maintenance window does not appear for some monitors in UI.
But when we do a GET for that monitor via api it shows multiple maintenanceGroupId assigned to it. Also the one which no longer exists./monitors/{id}
Release : SAAS
Component : APP SYNTHETIC MONITOR ENVIRONMENTAL
This is by design. The Maintenance windows are still attached to the monitor and also "visible" in the UI, when you use their id in URL, such as
https://asm.saas.broadcom.com/en/settings/maintenance-window/edit/111111
What makes it different to the one active,
https://asm.saas.broadcom.com/en/settings/maintenance-window/edit/222222
is that that one still has a Time Window waiting (to be active in the future), while the former two don't have any Time windows to get active in the future. We call this Maintenance window as "passed" and in that case it is not show in UI, unless it's marked as "Persistent". If a Maintenance window has the persistent flag checked, it's displayed forever.
ASM PM is considering some API changes to make it easier.