NYT and others I am sure have covered the launch hiccups..
https://nyti.ms/3wApWIE"Three of the four engines were fine but, in the fourth, a hydrogen line did not appear to open properly, and one of the engines was not as cold as the others.
This was the first test of the engine chill-down, which usually occurs 4 minutes 40 seconds before launch. Dress rehearsals of countdown procedures earlier this year were designed to catch such issues but were cut short by technical problems. As a result, the engine chill-down was not tested. But mission managers believed the rocket had passed the critical test objectives, and they moved ahead with preparations for launch."