I’m not an engineer, but this happened to us last year, so here’s what I learned the expensive way.
We bought 12 leak sensors for our hotels from a small vendor, LTE-M, certified module, all reporting to Hermetry. Three months in, all 12 went offline on the same morning. I only noticed because the Device offline alarms fired for every one of them within ten minutes, before breakfast. The vendor spent a week on it. It turned out the operator had started rejecting devices whose IMEI range (the first 8 digits, the TAC) wasn’t registered with them as an approved device. The module had its approvals, but nobody had ever registered the finished sensor.
What fixed it: the vendor went through the operator’s device approval, which for a product built on a certified module was mostly paperwork plus a short field test. Our TAC got added and the sensors came back the next day with no changes on our side.
So for your 300 trackers, I’d call the operator now, before the build, ask what their approval looks like for a product on a certified module, and get your TAC registered. And set up a Device offline rule on the tracker profile. Your trackers wake every 30 minutes over HTTPS, so I’d set the profile to Recent message with something like 1,800 s times 2 and a short offline delay on top, so you hear about a block the same morning.