If you are using pro-hosting tools please check if your multi-calendar works properly and let me know
My availability window is 3 months ( available until October 8. 2021). My monthly calendar shows it correctly and bookings are not possible after October 8. 2021. ..... but.... multi-calendar shows all dates available indefinitely.
I also have 3 months availibility window. You are right, the multicalender shows at first sight all dates are indefinitely available.
But... when you select 1 or more dates after 5 october (for some reason not 8 oct), it will show in the separate screen they are not availabe because of 3 months availibility window.
So visually it is indeed a glitch, but technically it is OK