Laser only cutting through top and bottom

"45%@700mm/sec."
That seems extremely aggressive for a diode laser. Perhaps it’s really 700 mm/min, which may still be too fast.

"why this may be happening"
Most diode lasers have a rectangular “spot” at the focal plane, typically wider than it is tall. If yours is like that, then:
Lines parallel to the X axis (left-right) cut faster
Lines parallel to the Y axis (front-back) cut slower
The only solutions:
More power
Less speed
More passes
Each choice has its own tradeoffs that you’ll discover as you try them out.