i do not know your gear+sensor setup.
But main problem with counting - speed and vibration.
If you use only one sensor and standard or HS Input - vibration at low speed generate false pulse and counter do not count correctly (+ count error present).
If standard input used - you can lost some pulse at high speed sensor activation (- count error present). HS input in single sensor mode can be used for high speed sensor activation but start stop condition also make some count error.
Best way for mecanical setup - use quadrature principle of measurement (you can read about it) and A/B shaft encoder HS input. Encoder with A/B output or two PNP sensor on the same special quadrature gear can be used.
This idea work with best result for low and high speed. Vibration do not affect on count result.
By the way as i see in your setup - two sensor used for mesure the same amount of data.
You can use only one sensor connected to two HS input chanel I0 + I2 at the same time and count/reset two HS counters separately.
Only one problem - HS counter backup ladder code needed. You can found V120 example in help project HSC directory.
How fast are the inputs counting? What is the Pulse duration?
Input 8 and Input 9 are NOT meant to be High Speed Counters.
( True - they can be used for Very Slow Counting applications with long input signals)
Inputs 0-1, 2-3, 3-4 ARE the High Speed Inputs. These Inputs can be Normal Inputs OR High Speed Inputs
High Speed Inputs are set up in the Hardware Configuration.
Look in Help -- High Speed Counters - to see how to set them up and the explanation of each option available.
Change you wiring to the High Speed Counter Inputs.
Also review the Installation Sheet provided with the PLC.