2 months prior to Comey being fired/Mueller being appointed, Nunes did the surprise presser about unmasking (Mar 22, 2017).
2 days after that (Mar 24, 2017), Comey made an unannounced/unplanned visit to the West Wing…spent about half hour.
No reason was ever given for his meeting with Trump.
He was never questioned about the meeting during his testimony, and there wasn't a memo written.