Problem was still in play this evening:
attempting to compile firmware
Compile failed. Exiting.
Server error
I upgraded particle-cli from v1.27 to 1.29 AND deleted the non-required .particle.ignore that I had added (refer to CLI Compilation - Flattening, Ignoring, Etc - #8 by UMD).
Problem solved!
I should have removed .particle.ignore. first before upgrading, but didn't.
What I did do was put .particle.ignore. back to see if this was the cause, got this:
attempting to compile firmware
Compile failed. Exiting.
Server error
Compile a source file, or directory using the cloud compiler
Usage: particle compile [options] [files...]Global Options:
....
Am 80% sure that the problem is the particle-cli version because .particle.ignore. was added after the problem had come up.
Case closed!
PS - NOTE that "Server error" comes up if you use wrong parameters in the command line, eg "particle compile photon -v"