Hello
I don’t work for Velleman, I’m just a hobbyist. I use K8200 which I have moded many times through K8203, K2804 and this year I have rebuilt 3/4 of the printer.
Here is a little more about the project:
I live in the UK but if you want send a prv and your configuration.h (I will check) , or think about changing the firmware to Marlin 2.0.x bugfix and in bugfixConfig you have firmware for most printers.
And in case of any problems I will help.
And with Marlin 1.x there were always problems (different versions of Arduino for different things) I had the same problems as you now. I am not able to check for you because I am now using the motherboard Mega2560 / Ramp1.4.