We're having the same problem.
We were previously running the ragnarok mod map.
We started getting this error with the new update.
I have:
1) Removed custom launch command line from control panel
2) Swtiched to official ragnarok map in control panel drop down
3) Removed map mod id for old ragnarok in control panel
4) Checked every mod ID on control panel to make sure they were all valid
When that didn't work I tried steamcmd and mod folder cleans from the control panel. That has not solved th issue for me.
Server ID 26992
According to this post the switch form mod to official maps is keep player structures saves dinos etc. https://survivetheark.com/index.php?/forums/topic/199625-ragnarok-unofficial-servers/
This would allow us to give users the link to the collection. With that they could pre install mods instead of hoping their connection doesn't time out in game. This would also allow us to use an existing user friendly interface (the steam workshop) to add/remove mods.
Also, I know of one specific problem this would solve. We ran into this problem a few days ago. It took hours for us newbie server admins to figure this out. One of the mods we had added was deleted by the author. This gave everyone trying to join a "Failed to install mod map" error. We had to go through our mods ID by ID to figure out which one it was. If it was a workshop collection, it would automatically display the mod as removed from workshop.
Please and thank you for your consideration.