Delta IV Heavy does damp squib show due to ground equipment

The ULA launch of an NRO bird has had it's issues. They actually got
to ignition on Saturday morning (the wee hours, EDT) but just as the
livestream host, one of their senior engineers, said "liftoff", the
engines were shut down.

quote
Instead of launching on time, ULA’s infrequently-flown heavy-lift
rocket was hit by 72 hours of delays to rectify minor pad hardware
bugs. Around 2 am EDT (UTC-4) on August 29th, Delta IV Heavy made it
just seconds away from liftoff before the rocket’s autonomous flight
computer detected an anomaly with pad hardware and aborted the launch.
As a result, the three cores’ three Aerojet Rocketdyne RS-68A engines
were forced to shut down after ignition – an uncommon Delta IV launch
abort scenario that has historically required at least a week of work
to recycle for another launch attempt.
/quote
URL:https://www.teslarati.com/spacex-falcon-9-doubleheader-ula-launch-abort/

This is expected to add a week to the pre-launch schedule, between
having to diagnose the issue and to get the launch vehicle ready again.

They had already extended their last hold by roughly an hour, for what
the audio seemed to say was a compartment thermal issue that they
decided they could live with, and the Aug 29 date was already a slip.
Several pre-flight articles around the web noted that the few launches
of DIVH made it hard to smooth out the routine, despite the maturity of
the Delta family (and there was B-roll during the hold of the history
of the Delta family, including the original Thor launches).

/dps "and DIVH has launched more times than SLS will"

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Trust, but verify.