There was an article in Structure a year or so ago, I believe, on light poles and specifically vibration and resonance failures. You may want to research that on their website.
Also, if you have any feeling this thing may become “legal”, you may want to have your discussions off this list only because an attorney could google your name and this could all become part of the evidence. Then they may try to discredit you using anything posted on this list, like why were you asking these questions if you are an expert on the subject… Not trying to be a jerk, I ask questions on here all of the time, but I have a lot of friends who are lawyers and I know expert witnesses that have been asked all kinds of things about their background.
I have a hard time believing that properly placed grout would fail because of compressive stress, just makes no sense at 4000+ psi, unless it was very poorly mixed. However, such a thin layer of grout sounds problematic, I can see a guy in the field watering that down pretty bad to get it into a small gap. Also sounds like it would be hard to pack in there properly without all kinds of voids and in general it is just too thin of a layer, not sure what the manufacturer would recommend but has to be thicker than that. I would not recommend repairing like that, plus how level does a light pole need to be? Would shimming with steel work? (Sorry I did not read the article, sounds like you got good input on the failure.)
HTH,
Andrew Kester, PE
Orlando, FL