The Good, the Bad, and the Dominatrix - S7-E23
Continuity mistake: When Sara takes the photos of Lady Heather's neck bruising you see 2 distinct ligature marks. When Brass serves her with the search warrant you can see only the remnants of one ligature mark, then when she is in Brass' office later she again has 2 ligature marks.
Mainstream - S3-E3
Continuity mistake: When Kitty goes to get a midnight snack, her hair is down. But a few shots later, her hair is up in a ponytail.
Continuity mistake: The establishing shot of the Agency's headquarters building zooms in on 3 tall, narrow windows recessed into a brick wall. We then cut to an interior view - of several wide, continuous windows without any recesses. They don't match the exterior windows at all. (00:07:30)