Near the end of the hold at T-10 the announcer noted that, in determining a new T0, the launch team had to consider "various cutouts in the launch window, varying from 1 seconds up to a minute".
In this launch window, which we're currently 26 minutes into, and it's 2 hours long, it runs until 3:04am Eastern Time, we have what's called 40 cut-outs, and in those cut-outs, they range from about a second to about a minute, these are times where can't launch. These cut-outs must be accounted for when determining a new T0.
I'm familiar with cutouts in the launch window due to unfavourable alignment of the Sun, Earth and Moon eclipsing the space craft too long, as explained in e.g. this NASASpaceFlight.com article:
Within the 10- to 15-day periods that have a daily opportunity to launch, there may be a day or two “cut out” by the 90-minute maximum eclipse time constraint for Orion. “Occasionally [you] have this odd seasonal constraint that comes along where the Sun is behind the Earth during the outbound transit to the Moon or during the return transit that [eclipse time] exceeds 90 minutes. And just the angle of the solar eclipse from the spacecraft’s standpoint causes an odd day to be cut out every now and then"
But those are multi-day cutouts.
What causes the very short cutouts in the 120 minute launch window?