Your description of the symptoms indicates that the power loss is between the PDB and the radio.
Things to check for:
- Loose connection or a wire whisker short at the wago connector at the PDB. If any copper can be seen, then redo the wiring there. Only insulation should be visible disappearing into the connector.
- Loose connections at any splices on either side of the 12v/5v converter
The multimeter test should show up either of the two preceding potential wiring issues.
Since three robots suffer from this I kind of doubt that the 12v/5v converters are the issue.
If the wiring seems good, then the next possibility is a loose fit of the barrel connector into the radio. Wiggle the barrel while powered on to see if it moves much. See if it can be wiggled enough to cause a power reset.