Thanks for the report.

Do you have reproduction steps for this issue?
Could you give some detail on how you set up the project with Noesis? Where is the NoesisGUI plugin located, and where is the Studio project located, is it in your Unreal project folder, or within a plugin?

For this usage, the plugin has been placed in Engine plugin folder. without any modification from the provided zip on the forum.
The studio project was located in a folder next to the Content folder (not inside it) so not within a plugin.

Regarding reproduction steps, this issue appeared for a full day after I did the initial installation of the plugin but the day after, after a computer reboot. the issue disappeared and i wasn't able to reproduce. However another colleague of mine was able to have it and it also disappeared in a similar fashion after a day.
It could be a cache issue but this unfortunately eludes me and do not have more precise reproduction step to provide.

Closing, as I am unable to reproduce.

Please reopen this issue if you experience this bug again.

I have reproduced and fixed this issue, being unable to open sample Studio projects, and being unable to create Studio projects, when Unreal returns a relative path for the project.

I have attached a patch with this fix.

Index: NoesisEditorModule.cpp
===================================================================
--- NoesisEditorModule.cpp	(revision 16380)
+++ NoesisEditorModule.cpp	(working copy)
@@ -618,7 +618,7 @@
 			return;
 		}
 		FString AbsProjectDir(FPaths::ConvertRelativePathToFull(FPaths::ProjectDir()));
-		FString PluginDir(Plugin->GetBaseDir().RightChop(AbsProjectDir.Len()));
+		FString PluginDir(FPaths::ConvertRelativePathToFull(Plugin->GetBaseDir()).RightChop(AbsProjectDir.Len()));
 		FString ProjectPath(FPaths::Combine(PluginDir, FString::Printf(TEXT("Assets/%s.noesis"), *PluginName)));
 		FString Assembly;
 		AddStudioProjectInternal(ProjectPath, Assembly, Order);
@@ -1091,7 +1091,7 @@
 			return;
 		}
 
-		FString StudioPath(OutFilenames[0]);
+		FString StudioPath(FPaths::ConvertRelativePathToFull(OutFilenames[0]));
 
 		if (!StudioPath.StartsWith(AbsProjectDir))
 		{

Hello,
I actually am experiencing the issue consistently now but I do not know what is the reason for it.
I am now using 4.0.0b6 and I have applied the patch provided.

Just to give a bit more context on how the Plugin is installed. I have installed noesis studio plugin as part of an Engine plugin (/Engine/Plugins/.../NoesisGUI). The actual xamls and noesis project files are located next to Content/, allowing for the automatic replication of the folder structure within Content/ to work).
I looked and it seems that no error message is being printed. I have an log message that looks like a problem but it doesn't sound related :

[2025.12.03-15.17.44:460][ 0]PIE: Unable to listen to input actions without a player controller in NoesisStudioInstance.

Could you check if moving the NoesisGUI plugin from the Engine Plugins folder, to the project Plugins folder, fixes this issue?