Certain panels can be really picky about sequencing or delays in the link training. I suspect there are mainly just slight differences in the programming sequences that some panels just don't like. The core link training code for DAL is here: https://cgit.freedesktop.org/~agd5f/linux/tree/drivers/gpu/drm/amd/dal/dc/core/dc_link_dp.c?h=amd-staging-4.7