The conditions described by the OP are similar to the issue we've had reported, with the only difference being in our experience the message and chime engage at 10 minute intervals not 20 minutes, and only then at highway speeds.
We have created an interim fix, all we've done is extend the chime reminder timer out from every 10 minutes to 360 mins (max). The chime will still trigger once at highway speeds, or, the if the Cruise Control is set, but then won't sound again until the truck is restarted.
Please understand this isn't our final solution and we are still continuing to work on a total silence solution, this however should make DPF deletes a little more tolerable.
If tests come back positive this will form part of our next software release while we continue to work on a more permanent solution.
If you require this fix before our next software release, all of our beta testers have access to this, so if they are your tuner it may be possible for them to modify your existing tune.
Cheers
Cindy