Why does Mikrotik break the connection with the USB modem at a certain time?

Question

USB

Mikrotik 2011, before 951 - from time to time the USB LTE modem disappears from the interfaces, in the "lte 1 link down" log. It appears immediately back, but at the same time, active connections like VPN have to be reconnected.
I noticed that there are several breaks per day at different times, but the vast majority of breaks occur in the interval:
05:11:47 - 05:11:53 (every day!)
13:14:27 - 13:14:47 ( 15 to 25 days per month)
And some more intervals that are less frequent.
U.P. The modem is connected via an active hub with thick high-quality USB wires. The modem itself does not turn off, its uptime is several weeks.
UP2. The firmware is now 6.40.4, but it does not matter - the stability of the modem crashes did not change from the firmware version.

Answer 1

The LTE network on the part of the provider is a very complex design, created to save sessions of mobile clients when switching from one BS to another.
Basically, these sessions are short-term, because most of the subscribers in the network are mobile phones and laptops with 4G modems.
Billing systems are also used in the mobile network - to write off costs and set restrictions for customers. These systems cannot make changes to already established connections, so once a day (usually at night) the connection is forcibly disconnected by the provider.
Depending on the operator, and the established conditions for breaking the session, sessions can also be torn during the daytime (for example, when a certain traffic is reached in one session), only employees of the operator network can give accurate information, but of course they will not do this))