Some of the logs generated incorrectly for some reason, which prevents from looking into what happens, when the disconnect occurs. If possible, could you generate another troubleshoot file?
As of now, looking at your settings, there are no indications of failing hardware, device picks correct APN and mobile signal characteristics seem good.
The disconnect might be initiated by your ISP, to assign you with a new IP address. As suggested previously, you could configure modem reboot on on such disconnect cases in Services -> Auto reboot -> Ping/Wget reboot, or configure a scheduled device reboot during every night in Services -> Auto reboot -> Reboot scheduler to try to workaround inconvenient disconnects.
If firmware was performed with Keep settings option enabled, please reset your device to factory default settings, as instructed here.
If previous options do not solve the issue, another option to try is to update your device's modem firmware. For this, you would need a stable alternate WAN source, either wired or wireless, and SSH access. I would provide you with the instructions.