NOTE: An updated version of this guide is available here: Diagnosing Cellular Connectivity Issues
Summary
Overview of basic network connectivity issue resolution.
Version
VERSION 20201215.1
This guide assumes you can communicate with the Notecard locally with serial, USB, or I2C and you cannot get the Notecard to communicate with Notehub via a cellular connection.
Check antenna connection
This seems trivial, but we have had many support calls where the issue was simply a bad connection between the Notecard and the antenna.
Check the co-axial U.FL connector is seated properly.
If the U.FL connectors were installed manually they occasionally do not seat properly and prevents the signal from getting through.
Ensure the connectors labeled “MAIN” is properly seated on both ends of the connection. These connectors are a little tricky to install manually because they are small and do not provide much room for error. When it does seat properly, you will feel it “click” into place.
Check out this guide as sparkfun for installation tips.
Ensure antenna signal not interfered
Antennas that are too close to metal objects or other devices that can produce electro-magnetic interference (EMI) may prevent establishing a connection to the cellular network.
For example, if using a Notecarrier-AF or Notecarrier-AL, ensure that there are no metal objects within the region labelled “keep-out zone”.
This represents an 11 mm cylinder around the black Taoglass antenna mounted on the board. You may consider elevating it from the table surface and moving it away from your laptop computer.
Try different location (signal strength issue)
If the signal reception is weak, then it is difficult to establish a network connection. Deep inside large buildings, metal buildings, shipping containers, or buildings designed to block wireless signals prevent the cellular signals from getting to the Notecard.
Try moving to a location where you can obtain stronger cell signals. For example, move close to an external window or outside in the case of large buildings.
You can make a basic assessment of signal strength using the card.wireless request, and looking at the "count" field in the response.
Capture trace log and contact support
A detailed trace log can be captured and provided to Blues Wireless support team.
We recommend you issue the following requests to the Notecard, and capture all the responses from the requests listed below and provide them to our support team here:
{"req":"card.version"}
{"req":"card.wireless"}
{"req":"card.trace","trace":"mdmmax","start":true}
{"req":"hub.sync"}
Wait several minutes for sync attempt to complete.
Request the recorded trace log with:
{"req":"card.trace","stop":true}
You can enter a support request sending a message with the 
icon, or support@blues.com