In my campaign I have several players that fall really heavily into "My Guy Syndrome" which is to say that they will excuse character actions that sabotage themselves and their teammates because its something that would be in character for their player character.
An example being that my teams sorcerer and rogue would actively be trying to sneak into a building to gather information while my teams monk will run into the building without a care exposing all of them and sabotaging the information gathering because it is in character for them to do that.
While I love having a dedication to your characters persona and I don't want to take that away, (after all that's a core aspect of roleplaying) my players keep on sabotaging each other in this way and no amount of mediation situations or teambuilding exercises that I put them in seem to help. Because their characters now have grudges against one another and its in character for them to snap at one another.
How can I 'delicately' bring this up to my players or how can I as GM create scenarios to help prevent this kind of behavior? How do I tell my problem players that they have 'My Guy Syndrome' and how can I get them to cut it out? The problem is that this behavior is ruining the experience for their teammates by sabotaging team plans and killing team dynamic.
This particular question was prompted by reading the comment thread "what is "My Guy Syndrome" and how do I handle it?" It introduced me to this concept however I noticed most of the solutions were for players and to help players realize when they need to stop this behavior or how to prevent themselves from falling into it. In particular I'm looking to find a solution on how a GM should handle this behavior when they see it happening in their game.