To answer your most recent question, a leaking hose on the differential pressure sensor pre-DPF would result in artificially LOW DPF pressure readings, or low soot mass readings. Now these ECMs do all kinds of rationality checks and such, and it's possible it's commanding regens because it's checking to see what's going on with readings it doesn't quite "like" but are still within spec for "good" readings.
Same goes for EGT sensors, if the exhaust temp sensors are skewed higher than actaul temps, but still in the acceptable and rational range the car can suspend the Regen that's occuring and then restarts it when it sees favorable conditions again. This can result in multiple partial regens.
There are techs who have a better understanding and more training on diesels than others. They will have GM Master Technician Certification in Diesel Performance. This certification is NOT mandatory, and most dealerships don't have a GM Master cert'd diesel tech. You may want to ask GM customer service to direct you to a shop that has one.
GM Master cert's are optional training. They require a tech to be fully trained in GM courses beyond the mandatory standard training, they require the tech to earn ASE certified in that area. And then beyond both standard GM and ASE certs the tech has to go to a hands on assessment course where they actually have to demonstrate their skills and knowledge in the understanding and repair of the system in question. You even get a certificate! LOL