I’ve also had a few instances of the DeepScreen appearing where you would not expect it.
For example, one-off appearances while uninstalling a legitimate program. Apparently,
the uninstaller triggered it.

What is the idea of behind DeepScreen? The programs I’ve seen that activate it eventually continue.
Why is DeepScreen activated? Is it because the programs have no “reputation” ?
There are always going to be programs that are not seen before that they are not recognized.

Is it based on some heuristic, something related to the behavior of the running program?

I can understand avast! trying to develop something like this, in my mind traditional AV has always been useless
against zero-day attacks. Some people have to “suffer” until the AV company can add the pattern to it’s database.