The LAN1 port link state changes come from the ESP device connected to the port, as it continuously initiates DHCP requests.
Could you try giving it a static lease, which can be done in the router's WebUI Network -> Interfaces -> Static leases page. Another option to try is to enable Force option in Network -> Interfaces -> [lan_interface] -> DHCP server -> Advanced settings.
Regarding mobile, within the first 15 minutes the troubleshoot has logged in, no mobile disconnects have occurred. However, there is a following warning coming from Auto reboot application:
ping_reboot.sh: Can't wget URL.
What, I assume, happens is that after 5 such failed attempts, device is rebooted. The reason being that option www.google.com, which might have been accepted in previous version, is not supported now and needs to be modified to http://www.google.com.
I also see that you have failover enabled, which appears to be unnecessary, as you are only using mobile interface and no wired WAN is connected.
In general, based on the configuration, I assume that you have updated your device from legacy firmware with Keep settings option enabled. My suggestion, to avoid any possible issues related to incorrect migration between firmwares, would be to reset the device to factory default settings and reconfigure it.
Best regards,