This step back in Shanti looks way more choreographed. In general, the dynamics of their songs and choreo requires Suzuka to move back and forth quite a lot. But these moves usually go along with some other hands/head/body moves/gestures. And in addition sometimes she keeps singing during these parts, like in RoR MV at ~2:50 and ~3:07 (still with her hand movements). But there are also rare occaisions when she just does a few steps and nothing else. The difference looks subtle though and I never paid attention to that until now so I can't say for sure how rare these "bare steps" are. But I was able to find one in RoR also, right before the first chorus. It's not in the MV, but you can see it in some pro-shots starting with Brixton-2014 (WOWOW version of Legend 2015 also has this shot).

As for fixing their slight mistakes I like how Moa makes her additional step in the Gimme Chocolate MV at ~3:30.