Hi Anna, great question. I have had similar experiences when I have conducted CLASS observations - three amazing cycles, and then one that isn't as strong as the others. This happens and that is why we suggest conducting several cycles - often 4 when you complete a formal CLASS observation. This ensures that no one cycle can have a significant effect on the overall score.
I understand the desire to conduct an extra cycle, to make up for the one that was lower in the Instructional Support domain, but that would but that means you aren't the same method to generate scores for all classrooms. Adding in an additional cycle for this one classroom could potentially inflate this one classroom's score.
I hope that helps,
Emily