NASA plans to return the superheavy SLS rocket to the Vehicle Assembly Building (VAB) to repair faulty components. This is stated in the message published on April 16.
The SLS was delivered to the LC-39B launch pad in March to conduct a dress rehearsal of the launch. As part of the procedure, the carrier was planned to be fully refueled, then the engineers had to work out the pre-launch countdown procedure.
In total, NASA made three attempts to refuel the rocket. None of them was completed due to various technical problems related to both the mobile launcher platform and the carrier. As a result, the leadership of the aerospace administration decided to return the rocket to the Vehicle Assembly Building. There, engineers will repair a faulty valve that prevented the SLS from refueling, and repair the connection of the mobile platform from where the hydrogen leak previously occurred.
Changes will also be made to the nitrogen supply system at the launch pad (it is necessary to ensure the launch). Before, failures were recorded in its operation several times, leading to the postponement of the refueling procedure. It is worth noting that NASA believes that the situation with the SLS is not something extraordinary, and cite as an example the first flight of the shuttle, before which the winged ship had to go through five or six launch rehearsals.
According to https://spacenews.com