OK, I've read through the entire thread...
To me, this sounds like an infection. A re-occurring one.
When asked about your cleaning and sanitizing practices, you always say I sanitize like xxxx.
Cleaning and sanitizing are two different things.
....
This post is absolutely on point. I used to think I cleaned & sanitized well before I had some problems early on. Then the guy who got me into brewing came over to eyeball my process and pointed out 5-10 things I'd never even considered when it comes to cleaning/sanitation process. Now I keep a squirt bottle of StarSan with me whenever I'm doing brewing/beer stuff, and I spray the living **** out of every possible surface. Have only had one problem since, and it was from repitching on a used cake in a carboy I didn't stopper for a few hours.