In regards to license issues, the smoking gun(s) have to be some assets that are licensed under a CC-BY-NC-SA license, NC meaning no commercial use. The following mods `farming`, `water_life` and `motorbike` contain one or more assets licensed as CC-BY-NC-SA.
>>> grep -ri 'CC-BY-NC-SA' mods/farming/license.txt:Created by RZR0 (CC-BY-NC-SA) mods/water_life/doc/license.txt:CC-BY-NC-SA 3.0 by Melkor mods/motorbike/LICENSE:Melkor (CC-BY-NC-SA 3.0)
While you could make the argument that you can in fact sell a game containing mods licensed under various GNU copyleft licenses completely legally (you just need to respect the licensing, i.e. keep the mods under a compatible license and give attribution), adding mods that contain assets that are licensed to EXPLICITLY NOT ALLOW COMMERCIAL USE (i.e. selling the game for profit) is completely illegal. You were notified of this by multiple people but never removed these mods or replaced the assets that are being used illegally.