NSCLIENT\NRPE doesnt handle arguments with white spaces
This was my problem, I forgot to add double quotes to the arguments IN the NSCLIENT itself. FACE PALM
Just for a reference:
test = cmd /c echo scripts\\test.ps1 $ARG1$; exit($lastexitcode) | powershell.exe -command -
Should be:
test = cmd /c echo scripts\\test.ps1 "$ARG1$"; exit($lastexitcode) | powershell.exe -command -