If it’s any help, the same thing happened to me.
I was booked to CV in March and periodically checked the booking to see if flights were still operating. At some point last Autumn, I noticed I could no longer book my flights. I rang TUI and they said there was nothing to worry about.
6 weeks later, we got an email to say our flights had been cancelled and they gave us an option to rebook or cancel.
I would guess the booking engines change before people get official notification so this could be the same for you.
In our case, holidays were still on offer but the frequency of flights per week was being scaled back so we could still have gone if we changed our dates by a day or two.