All good ideas and very basic troubleshooting with which the OP may be really familiar. Part of the problem about working through a technical issue in an on-line forum is that the flow of information is very choppy. I have seen this (and participated in it) many, many times. Test steps get left out, participants believe obvious steps have been taken when they have not, and everyone troubleshoots and fixes things in a different way (ask my car guru to speak on his opinion of my troubleshooting of vintage car issues. He will tell you flat out).
So true, when I’m doing on site troubleshooting at a service call being able to pick up on small nuances can some times lead to the problem cause and solution.
Just like a car when someone says their sound system is making a noise not until actually hearing the type of noise do you have an idea as to where to look for the problem.
Yes I work on cars to!