Code disappears in target branch on git merge w/o any indication

Question

I'm having a problem with Git merge. In short, I'm merging the master branch into a feature branch, essentially git checkout feature && git merge master.

This is how it looks graphically:

other branches            O1 --- O2 --- 0x
                            \      \      \
master                       M1 --- M2 --- M3
                               \             \
                                \             \
                                 \             \
                                  \             \
feature                            F1 --- F2 --- staging
                                          ^           ^
                                          |        same code missing here
                                     code present here

What I cannot understand is that:

• commit F2 is checked out. The code is present in a file.
• I make a merge, there are conflicts (including in the file with the code in question). At this point the code is already missing w/o a trace. I searched with grep over the whole project and in the file where it's supposed to be.
• If I resolve the conflicts and commit, the diff of the commit doesn't mention the code removed at all.

Could anyone explain please how this can happen? My intuitive understanding is that if Git removes something it must be reported in the diff at least.

I'm having a feeling that this may have something to do with different merge strategies. But I still can't understand how Git could remove something and not show it in the diff.