Thank you so much for playing the game and commenting! And the encouragement!
I actually had a fix before UE crashed and I couldn't recover a chunk of fixes and had to press on for the jam deadline! I guess I did movement similar to you then, I used a timeline with a sigmoid curve and lerped location and rotation. Both were snapped to a grid but I didn't do that well I think!
But I had two solutions in mind:
The one I lost and didn't readd (everywhere) rotation was locked to cardinal directions i.e. ControlRotation Yaw was Snapped to Grid(Rotator) set to 90.0. This worked but I had to know when to do it and I didn't do it everywhere! In hindsight I could have just put this in tick since when bIsMoving wasn't happening!
I dropped this idea becuase it was unpleasant to play: During timeline run a bool bIsMoving was true and this blocked input being acted on (stopped people pressing x during the turning). It made it feel laggy, in hindsight I should have set the timeline run time to 0.5 seconds and kept this lock out.
The snapping has a issue though, my map wasn't quit setup perfectly along the axis and I think that resulted in my zigzagging movement(which also used snap to grid size).