We recently OnBoarded a few 1909 machines to ATP which went fine and they started to send sensor data during a couple of minutes but after that no more data is being populated inside of the portal.
We are currently sending the sensor data through a forward proxy without authentication and everything whitelisted that needs to be whitelisted. In fact, 1809 machines with the same GPO that configures the TelemetryProxy works without any issue.
Looking through the logs SENSE claims that it has sent sensor data with success, i.e it has tried to send sensor data 12 times and succeeded 12 times. Even looking at the Proxy logs we can see the machines sending data but nothing gets populated inside of the portal.
As soon as we bypass the proxy it starts populating sensor data once again.
I've seen other reports of people having the same issue but havn't been able to find any solution nor acknowledge of an issue.