g_fullbrightplayers 1 doesn't make player models bright enough (compared to the legacy megaerebus)
This issue was discussed in #xonotic.pickup today and few people reported that they get it on their systems.
I made a quick video demonstrating the problem. First I start with g_fullbrightplayers 0, then I set it to 1 and call vid_restart (which results in no visible difference). sv_allow_fullbright is set to 1. Then I set the model to megaerebus and it immediately works well (even without vid_restart).
The version of xonotic that I use is xonotic-v0.8.2-727-g61659a08~ (autobuild).