Most CMMSs were built to maintain machines inside a factory, where an asset's location is "Line 3, Bay 2". When a customer's assets are spread across an entire province, a map gets bolted on top: an address field and a handful of markers that slow to a crawl as soon as the inventory grows.
We built it the other way round. First the real geometry in PostGIS, road routing, optimisation and the base map, all inside the installation. Then, on top of that, work orders, shifts, the warehouse and costs. That's why you can browse more than 100,000 elements without paging or filtering, and why your staff's positions never go out to a third party's API.
Behind it is AvantGeo, a geospatial engineering firm that has been putting systems into production since 2008 for electricity distributors, water operators and solar plants. That's where the app that works without coverage comes from: years of field data capture in substations, wastewater treatment plants and sewer networks.
The complete functional documentation is public, and you can use it to check what the system does. What it can't tell you is how it fits your operation. That takes half an hour to see, on a case like yours.
For your IT department: mapping, routing and optimisation run inside the installation, in European Union data centres; the API is open and full export of your data is always included. The details are in security and data governance.