

An impeachment conviction results in removal from office. The previous impeachment proceedings did not result in a conviction.
(Edit for additional information: While an impeachment uses terms like “trial” and “conviction” it is not a judicial proceeding. It is entirely a legislative proceeding which is formatted to resemble a judicial one, but is not bound to judicial procedure and it also can not produce a criminal conviction or sentence.)
The immunity regarding official acts pertains to judicial proceedings. An impeachment is a legislative proceeding. While it uses judicial terms like “trial” it is not the same thing and can not directly result in criminal conviction or sentencing.