Hello,
I'm sorry to hear that you're experiencing issues!
I will ask you to replicate the issue (wait for the mobile connection to drop), then navigate to System → Administration → Troubleshoot and generate a troubleshoot file. It can be attached to the original question and will only be visible to Teltonika moderators.
The DHCP lease issues seem to be related to the loss of the 4G connection, can you verify this? Or does it happen randomly? Could you explain what the exact issue with DHCP is?
Best regards,
DaumantasG