I also had the same issue, as did our custom servers in the Oceanic region.
The solution to this issue is:
To copy the MultiplayerForcedAvatars from your Mount & Blade II game directory, e.g.,:
C:\Program Files (x86)\Steam\steamapps\common\Mount & Blade II Bannerlord\Modules\Native\MultiplayerForcedAvatars
And copy and paste those files to the following path:
'C:\Program Files (x86)\Steam\steamapps\common\Mount & Blade II Dedicated Server\Modules\Native\MultiplayerForcedAvatars'.
Your server should now be operational when you run your .bat.
Please let me know if it isn't.