Why does HTTPS take a long time to load after re-registration in the network of a cellular operator?

Question

mobile connection

The question has been bothering me for a long time. After rebooting the cellular modem, or after changing the type of network, in general, after re-registering in the network of the cellular operator, for some time sites using the HTTPS protocol do not want to load for a long time (they hang waiting for a response, or sending a request). After about 30 seconds - 1 minute everything is back to normal and they start to load quickly again. At the same time, this is not observed with sites on HTTP.
What is the reason for this behaviour? Does it have something to do with DPI technology? :)