They themselves said "..this unreleased version caused issues". That could be referring to anything - including service-overload issues but I don't know why that would be that surprising.
This is exactly why companies like to have tight control of the roll-out of new products. They want to find these types of bottle-necks and glitches in rather controlled environments.
If this isn't a service-overload issue, I'm having a hard time imagining what kind of problems this unreleased Android version could have caused.