@Private:
Apparently Beatty lost contact with a significant part of his own force which could not see his signals, which resulted in his having fewer ships to hand when he met the German battlecruisers. He ignored the more modern communication means at his disposal.
I assume that the “more modern means of communication” mentioned by the documentary is a reference to wireless telegraphy, since Beatty’s ships seem to have used both blinker lights and flags for communication. W/T in WWI was a mixed blessing in combat, so Beatty may have had valid reservations about using it. Automatic devices allowing messages to be encrypted and decrypted instantaneously didn’t exist at the time of WWI (nor even in WWII, as far as I know; the Enigma machine was painfully slow), so in a fast-moving tactical situation in which information is very time-sensitive messages would have had to be sent in the clear, because encyphering by the sender and decyphering by the receiver is too time-consuming. And the problem with sending any kind of radio (or in this case radio-telegraphy) messages is that the enemy will be able to pick them up too. W/T sent in the clear therefore potentially informs the enemy of your position (through direction-finding) and intentions (by analysis of the content of the message). You could make life more complicated for the enemy by sending uncyphered messages whose content consists of coded instructions taken from code books (like, to invent an example, “Perform maneuver X-12 immediately”), but there’s always a risk that the other side’s intelligence services have acquired or reconstructed your codes.
At any rate, part of the problem which Beatty apparently had at Jutland was that his force included a squadron that normally operated with Jellicoe’s battleships rather than Beatty’s battlecruisers, and whose commander wasn’t informed that Beatty’s standing orders on what to do in such-and-such a situation weren’t the same as Jellicoe’s standing orders. As a result, that squadron seems at one point to have done something different than what Beatty was expecting it to do, which resulted in Beatty temporarily losing the concentration of ships which he had had up to that point.