Turn down the acceleration and max speed 90%. If it solves the problem start increasing the speed until the problem comes back. At some speed(s) there can be resonance in de stepper driver causing irratic movements. I test my max speed by very very slowly increasing the speed. You can than hear the resonance. Every time you pass this speed (during accelerations), you may lose steps. Lowering the power supply voltage may solve this problem.
In my software if found the next lines, added once i solved a similar problem:
//According to GRBL config.h: !!!!! MinStepPulseTime + direction delay time must not exceed 127 !!!!!!!
//Found that running at 70 us results in slow max FeedRates
//keep lower than 35 us for good results
I also have a chinese board with a realy bad design (Smitt Trigger before the optocouplers). I bypassed the optocouplers to get it working.
I use TB6600 drivers (TB6560 also). Some say that leadshine drivers are better (getting more speed) but if you don't want/need to get the most speed from your machine, i thing the cheaper drivers will do. What i have read on several forums is that Gecko drivers are the best. But for those you pay top dollar. As soon as i have the time, i am going to build my own driver, i bit like smooth stepper and Gecko, but based on TB6600.