[solved] Gateway pending after dynamic Prefix changed

[Bob.Dig]

So first, I am not searching for an alternative solution, like getting a HE-tunnel or a true modem, just want to describe the current problem and maybe someone has a solution for it.

pfSense is behind another router which has a modem and makes the internet connection. A dynamic prefix (/60) gets delegated to pfSense and everything works fine until there is a reconnect after 24 hours on the internet connection. Then the gateway in pfSense will loose its connections and is not coming back on its own.
But if I later change one thing in the gateway settings, even only the monitor-ip, it is instantaneously coming back.
So I guess, right after the reconnect the connection is not yet up and pfSense will not try any further? Is there something I can do about it, maybe running a script at a given time, because the reconnect is always early in the morning.

[Bob.Dig]

A̵ ̵c̵r̵o̵n̵-̵j̵o̵b̵ ̵(̵/̵u̵s̵r̵/̵b̵i̵n̵/̵n̵i̵c̵e̵ ̵-̵n̵2̵0̵ ̵/̵e̵t̵c̵/̵r̵c̵.̵r̵e̵l̵o̵a̵d̵_̵a̵l̵l̵)̵ ̵s̵e̵e̵m̵s̵ ̵t̵o̵ ̵d̵o̵ ̵t̵h̵e̵ ̵j̵o̵b̵.̵