ALJ did not have sufficient substantial evidence that the regulation was violated; the enforcer of the rule has the burden of proof, and while every violation need not be personally witnessed, a violation can't rest on speculation and conjecture where there are several possible scenarios.
http://media.ca8.uscourts.gov/opndir/18/07/172281P.pdf
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.