Undocumented cell mass

Had my frozen embryo transfer today and the embryologist mentioned there was an “undocumented cell mass” or mass-like area around the embryo. They still transferred it and specifically said there was “no grading change since freeze,” which I took as reassuring, but now I’m spiralling a bit wondering what it actually means.

The embryo was a frozen blastocyst with assisted hatching. On the photo there’s a darker clump/mass on one side of the embryo that I can’t stop focusing on. The clinic didn’t seem alarmed and didn’t downgrade the embryo after thaw.

has anyone seen something like this before?! what does it mean??!!!!