This guide is here to provide various solutions to problems encountered in GM mode. If you don't find the solution here, please post it in the comments.
When refering to the installation folder, it's :
When refering to the mod folder, it's :

Probably the most common problems encountered in GM mode, especially if you use mods.

Cause : the player(s) miss one or several mods.
Fix : make sure that the player(s) have all the mod paks and the same versions than the GM.

Cause : same than Issue #1, can also be caused by the GM not having Norbyte's script extender but the player have or vice-versa. Can also be caused by the presence of the meta.lsx file in if the GM do not have it or vice-versa.
Fix : same than issue #1, make sure that everyone have Norbyte's script extender and make sure that everyone have the meta.lsx if the GM use GM Player Limit Increased mod, or that everyone remove it if the mod isn't used.

Cause : same than Issue #1
Fix : same than Issue #1

Cause : the affected player and/or the GM have a poor connection speed.
Fix : if it's only one player, then someone else can start a second instance of the game and join to create the character. Join the game, and leave the second instance of the game. The player triggers long black screens should be able to join and take control of their character without problem.

Cause : the campaign is heavy and the players and/or the GM have a poor connection speed.
Fix : if you use custom vignette images, make sure to lower the resolution and the quality of the images to make it lighter. Also restrict the numbers of scenes as much as possible. To delete custom images for Vignettes and Maps, go in They are located into Vignettes and OverviewMaps folders.

Cause : Issue known since Gift Bag #3, caused by mods not automatically loaded when loading a save.
Fix : Make sure to make your mod list in the main menu matching the one from the GM save (e.g. save mods activated in the same order). A quick way to do it is to load into prepare mode a campaign that have the same mods (usually the same campaign). You can also use the mod manager to save the mod order and restore it before playing.

Cause : Issue known since Gift Bag #3, reason unknown.
Fix : just save and reload.

Cause : Most likely related to data mismatch between players and GM mentioned in Group 1 - Issue 1, but it can also happen randomly. Can also be caused by a mod update/removal.
Fix : If it's not because data mismatch, then make one or several players leave the game and rejoin. The scene should load fine and the players should be able to re-join without problems.
Can also be fixed by saving and reloading sometimes.

Cause : Issue known since Gift Bag #2, reason unknown
Fix : In normal cases, the main menu mod list is independent from the GM one. However in this case, you need to make the mod list of the main menu match the one from the GM save. Then, try to load in, then save, load that new save and see if the mod have been activated. If not retry. If it's activated, then save again and reload. Now try to load in a different scene. If it's stuck, then load at the last save and try to save/load several times.

Thanks to the modding community to point out some issues and thank to Norbyte for parsing the crash dump to better understand how that mysterious forest GM mode is.

This guide has been created as a reference for the DOS2 GM Bastion, a Discord server dedicated to the GM mode : https://discord.gg/zBZ9bme