It still had problems during the return flight, i.e. additional unexpected component malfunctions, but not serious enough to prevent a successful return. There

It still had problems during the return flight, i.e. additional unexpected component malfunctions, but not serious enough to prevent a successful return. Therefore the decision to not use it until the causes for all such malfunctions are understood was completely justified. Problem: "one of the Starliner’s reaction control system (RCS) thrusters did not function". Why it was not serious: "there are plenty of backup RCS thrusters". Even if the redundancy ensured a successful return, the causes must be understood, because otherwise at a future return more than one thruster could malfunction and the redundancy may be insufficient.