The Battle of Britain Five Months That Changed History, May—October 1940 by James Holland (z-lib.org).epub

Yet although the bulk of Army Group A was thus a sitting duck for any
Allied aerial attack, no such assault came. On the night of the 10th and
again the following morning, Allied reconnaissance aircraft spotted a
number of German columns going through the Ardennes. Although
reported, this was not taken seriously. On the night of 11/12 May another
recce pilot reported lengthy columns of enemy vehicles, but this too was
treated sceptically. On the afternoon of the 12th yet another reconnaissance
pilot reported the same, but although his claims were passed on to the
intelligence section of the French Ninth Army, it was dismissed as being
absurd. And so a golden opportunity to smash Army Group A went
begging…
While the Allies had obligingly played ball in Guderian’s drive to the
Meuse, he was now having a few difficulties with his commanding officer,
von Kleist, who was insisting on interfering with plans for the crossing.
Guderian accepted von Kleist’s order to attack across the Meuse at 4 p.m.
on 13 May, but disagreed about where exactly this attack should be made.