MECM | During install Clients switch from Intranet to Internet and stop installation

[LinPie]

Hello there,

we are currently on Config Manager Version 2309.
We have a CAS and multiple Primary Sites.
For each Primary Site / Location we have mostly the same Windows Installation, only Domain Join and maybe device drivers are different.
The Config for each Primary Site is the same, only one Primary Site is SSL enabled and can communicate with our Cloudpoint.

Within on Primary Site / Location (which is not the SSL one) we have a problem installing clients in our second domain.
This primary site is for two networks, one "Administration" network and one for our students (second domain), so different domain but everything else within Tasksequenz is the same.
Domain Join works, Clients are communicating with the primary site and everything seems to work fine. After installing and configuration of the Config Manager clients on these clients the windows installation should go on with installing software and perform scripts and things.
The installation of software is not working with generic error, so we enabled to go on. Installation goes on and goes into error 0x80070002 while trying to access a network path to execute a script.
As far as I can see within the log the problem is not the permission of the user or that he can't reach it (the user is the same on all locations and is working in second domain). The user is also within configuration of the MP / Software Distribution as Network Access Account.
It seems that he suddenly can't find the package/tasksequence - I see within "ClientLocation.log" that the client has the correct MP assigned and is in Intranet. Suddenly this changes to "Client is in Internet" and "Current Internet Management point is <empty>". This site has no Internet activation yet so I'm wondering why these clients are switching? It happens within 4 of 5 Installation, so 1 Client is not switching automatically in this network. Within the other network at the same primary site everything works perfect.
Where can I see why they are changing to Internet? They are permanent on LAN.
Where can I set that they should only use Intranet (and why do I have to do this only for this site and this network)?

Only with this site and this network we have the problem that sometimes clients are falling out of their collections are not approved any longer, makes sense now if they are switching to Internet and have no connection to the MP anymore.

 

EDIT: It was working properly 1 month before and we made no change as far as I know....

If anyone has any Idea or needs more information I would be glad.
Thank yall in advance.
Lin

Edited August 29 by LinPie