Many unavailible device

Добрый день!
Поставил на монтиоринг количество устройств в системе
Количество устройств я получаю по АПИ /api/devices?all=true

Среди полученных значений есть доступные и недоступные устройства
На приложенном графике есть прямая корреляция между доступными и недоступными устройствами
Подскажите по какому признаку устройство считается недоступным?
Можно ли как-то снизить количество недоступных устройств за счёт каких то счётчиков или таймеров?

Good afternoon
Put on monitoring the number of devices in the system
I get the number of devices via API /api/devices?all=true

Among the received values there are available and unavailable devices
In the attached graph, there is a direct correlation between available and unavailable devices
Tell me on what basis the device is considered inaccessible?
Is it possible to somehow reduce the number of inaccessible devices due to some kind of counters or timers?

Screenshot - https://disk.yandex.ru/i/yBJpHqwxA1V2FQ

What do you mean by unavailable?

status "offline"

Offline means that the device is not connected to the server.

Okay, thanks for your answer

Could possibly be that the server or the database can't handle the incoming messages 'flow', and some devices might not get registered as online. But that must require a really big amount of devices or a very weak machine.