I just answered this for someone else and I have had this problem for months…of course make sure you have no special characters and do not make your patch notes in the dev kit uploader and try to upload. If that doesn’t work…
you are in an unfortunate place some how your .vdf has been corrupted, but here is how I fixed this … warning it sucks.
open your mod page in the steam workshop and right click copy page url and paste to a text editor to get the PID the numbers at the end…if you don’t know it already.
In the dev kit upload dialog ‘reset publisher’
upload to steam as a hidden file
log out/ exit steam completely
open file - #:\Epic Games\ARKDevKit\ModTools\ModConfigs’modname’.vdf in a text editor and change the PID back to your original one and save the file.
go to your - #:\Epic Games\ARKDevKit\ModTools\SteamCMD\ directory and launch steamcmd.exe
type - login ‘password’ ‘login’
type - workshop_build_item #:\Epic Games\ARKDevKit\ModTools\ModConfigs’modname’.vdf
type - quit
close the window
open steam and delete the extra hidden mod
where ’ ’ is your own information and #:\Epic Games\ARKDevKit\ is your complete dev kit path including drive
you will have to follow this process with every update from now own unfortunately.