Here it is:
/DBlAAAAAAAAAP/wBQb+GVJTDABPcAZNRFNOQzUCRUNVRUkAAKTff8MAACky4A8xdXJuOnV1aWQ6QnJlYWstQjAwMjA4NTU2ODlfMDAxMi0wNy0xMC1YMDExMjUxNjEyNDAAAPkSB7E=

This is valid SCTE-35 found in the wild (in a DSM-CC stream).
It is perfectly parsable with https://comcast.github.io/scte35-js/

For reference, this is the code the HbbTV app uses to parse it:
http://hbbtv.mediaset.net/app/mplayhbbtvgoldzoo/dev/js/component/scte35Parser.js

Looks like threefive doesn't have support for custom descriptors maybe? It seems to define a custom tag=0x70 descriptor.

I tried to do something like this: https://github.com/futzu/scte35-threefive/blob/master/examples/upid/custom_upid_handling.py
but unfortunately it doesn't work since as soon as threefive sees the unhadled tag=0x70 descriptor (not in known descriptor map) it refuses to parse extra stuff. After that there is a regular tag=2 descriptor but it gets ignored, and I get an empty descriptor array in the end. @futzu I guess this last one is a bug, it shouldn't ignore known descriptors.

I'd like to custom-process the tag=0x70 descriptor AND get the content of the tag=2 one