In some locations, there may be internet connectivity "dead spots". Typically these may be in a downstairs area, or outside of your location, and therefore do not have a WiFi or Cellular signal.
In this case, the best strategy is to start your checklist/s and Exit. They will then move to In Progress.
You can now go to where you need to and complete the checklist. The device will be in Offline Mode while you complete your check as it will not have internet connectivity.
Once the checklist is completed it will be flagged as Not Sent.
When you are back in range of internet connectivity, it will then upload the completed checklist/s (you may need to refresh or select Not Sent).