Who at the FBI expressed "concern" about releasing the memo? It apparently wasn't Wray:

It is important to note that the statement was unsigned, not under the name of FBI Director Christopher Wray or anyone else. The statement is at odds with what White House chief of staff John Kelly said earlier Wednesday. The discrepancy is unusual.

https:// www.cnbc.com/2018/01/31/fbi-says-it-has-grave-concerns-about-accuracy-of-house-fisa-memo.html