Intellisense doesn't work

Hi,

I know this issue has been addressed in other posts but none of the solutions tested worked for me. I tried the solution of this post : Intellisense stops working when installing new nRF Connect for VS Code extension - Nordic Q&A - Nordic DevZone - Nordic DevZone (nordicsemi.com) 

But instead of doing Pristine build that doesn't work for me (maybe because I have custom firmware with CMake preset?) I removed the build configuration and re-added the build configuration and then Build. Could you confirm this is equivalent to a pristine build ? 

I also tried to add 

"C_Cpp.default.configurationProvider": "nordic-semiconductor.nrf-connect",
to my settings.json. I tried to uninstall/reinstall nRF Connect extension pack (along with closing/opening vscode). None of this work on the long run.
Sometimes, I make it work I don't know how, and then, it breaks, I don't know why. I uninstalled C/C++ Extension pack that I believed was causing conflict but the issue remain.
is there any other extension that could cause conflict? 
 
Is there an "always work" solution? I can re-do what I already did if needed and if step by step instructions are given. 
Thank you for your help
EDIT : I tried a from scratch installation : uninstall most of the extensions (except python and non related C/C++, make, gnu, nrf, mcu etc...), uninstall vscode, restart computer, install vscode, install nRF Connect extension pack ONLY. It doesn't work. But I noticed that it is specific to a projects. With some projects, it works, and other, it doesn't. One of the non working project is a folder where I import samples only : 
On my custom project, I just realized that removing build configuration of a working project breaks Intellisense, even if I re-add the build configuration and I build the project (that builds successfully). Why?
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