So I solved the problem. I apologize if this sounds abstract without screenshots, but here was the issue:
My blueprint network looked a little like this.
[Press Y Key] → [Get Y Rotation of Actor] → [Set variable “y_rot”] → [(Some timeline lerp nodes to control the rotation animation, referencing “y_rot”)] → [Set actor Y rotation to ‘y_rot’] → [Set ‘y_rot’ variable to new y rotation of actor]
I did some debugging by adding two [Print String] instructions to two different inputs. One of them printed the rotation value of my actor, and the other input printed the float value in my “y_rot” variable. In theory, they should always be the same. I then changed the increment of my rotation command to 20 degrees (down from 90). So each execution would increase the rotation on the Y axis from 0 to 20, 20 to 40, etc.
I found that once this value exceeded 90 it would “invert” the value (for lack of the proper math term). So I would press the Y key to advance the rotation from 80 to 100, and after that my two [Print Strings] would disagree: one saying 100, the other saying 80. Further presses of Y repeated the same rotation from 80 degrees to 100, over and over.
I removed the first [Set variable “y_rot”] node from my network and it solved the problem.