Yes, this is a custom board using MK66FN2M0VLQ18, and a MK20DX128VFM5 with OpenSDA v2.2 bootloader and DAPLink rev0244 firmware.
There are more than 80 students in the class, and for most of them the DAPLink debug probe works fine on their computer, but the problem mentioned above pops up on some computers persistently.