ME3 NG+ Garrus Romance - glitch?

Hi.

I can't find an answer to this *anywhere*.  I'm trying to do a completionist NG+ playthrough of ME3, but am encountering a problem I haven't seen before.

Issue: Garrus romance can be started (during the initial conversation early in the game) but then unaccountably breaks at some unknown juncture, leading to "friend" dialogue during a certain scene on the Citadel.

Background: Xbox 360, all SP DLC installed, NG+ Insanity playthrough with Lvl 60 Shep, originally imported from ME2 with all required plot and romance flags.  Import did not glitch and the romance "worked" in the initial ME3 playthrough.  Did not start Leviathan questline prior to the scene on the Citadel (or any other DLC questline, for that matter).

This has now happened to me twice, so it's got me curious. Does anybody know if this is Leviathan-related (as suggested by a few posts on BSN) or due to the playthrough being NG+?  I can't work it out. ⁊_⁊

Thankage.