Most shifting issues can be attributed to an out of adjustment derailleur.
The common issues include
- Skipping gears
- Delayed gear changes
- Extra noise
- Chain falling off
For more information Park has a complete write-up on the job: https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment
If you are still having trouble, please submit a support ticket using the same email you placed your under. Please note in the ticket your Biktrix order number, the trouble you are experiencing and include photos of the issue.