Stepper motor Speed

What you are seeing is probably a limit to the speed with which steps can be generated. Once the system hits the maximum step-rate the system will realise that the machine is out of position and trigger a following-error.

What is your step length and step space? Add them together, and divide into one second. That's the maximum number of steps per second that the system can generate. You are probably hitting either this limit, or the limit of the base-thread speed, as the system can generate at most one step per base period. (If you don't see a "reset" function in your HAL then it is one step every two base thread cycles.

If the driver can handle it you can try reducing step length, or the base thread period. But you might find that the only answer is to change the microstep ratio.

I haven't been able to find what sets the step length and step space for Remora.
At a scale of 1280 steps/mm and a speed of 1800 mm/min you need a step rate of 38kHz. Most stepper drivers are fine with 100kHz (5000ns step and space) and many can go much faster.

I do see a PRU_base_freq setting that defaults to 40kHz. If that is the limit you are hitting then you should be able to manage 1875 mm/min.
If you can do 1870 but not 1880 then that is probably it.