Your website calendar can show dates as available (green) even though they are blocked in your PMS. This is a display issue only.
Why this happens. The website calendar renders from a locally synced copy of your calendar. If the site’s sync backlog is delayed, recently added blocks can show as green until the sync catches up.
Why guests cannot book these dates. Every booking attempt is checked live against your reservation system at the moment of booking, so no guest can actually book blocked dates. This live check is what produces the "business restriction" error when someone tries to book them. There is no double-booking exposure.