Hey @rit, thanks for the tip, it worked perfectly for me !
What I did is inside a BlueprintFunctionLibrary, I have the following
BPFL.h
UFUNCTION(BlueprintCallable)
static void flushInputs(const APlayerController* PlayerController);
BPFL.cpp
#include "GameFramework/PlayerInput.h"
// ...other includes and code for other things...]
void UBPFL::flushInputs(const APlayerController* PlayerController)
{
PlayerController->PlayerInput->FlushPressedKeys();
}
This gives me a node inside blueprint that I can place before or after the Input Mode.
And that fixed my issue !
Thanks again 