Unsafe context not kept

Hi,
I am working on a Unity 2018.1 project in Rider and I need to allow unsafe code since I have to use an external c++ dll which uses pointers. My problem is: every time I allow the use of unsafe code from the Project Properties window (both in Debug and Release) it works for 30 seconds then, as I switch file or window, it gets back to being not allowed and I have to open the Project Properties again and again to keep allowing it. I tried manually changing writing <AllowUnsafeBlocks>True</AllowUnsafeBlocks> in the csproj file but it's always brought back to <AllowUnsafeBlocks>False</AllowUnsafeBlocks>.

Is anyone else having the same issue?