SpaceX has not provided details regarding the reason for the delay. However, observers noted that on the night of January 10 to 11, following a fueling test, the upper stage of Starship — the S33 craft — was removed from the Super Heavy B14 booster.
After this, engineers inspected the thermal protection of the S33 while the Super Heavy B14 technicians worked on the booster valve covers. The system was then reassembled.
The launch notification for Starship from the Federal Aviation Administration is valid from January 9 to 18, giving the company at least two more days to proceed.