Remind me, the LP EGR cooler is the one for the big turbo, correct? The LP EGR valve might be the root cause. If it's not actuating there will not be a temperature drop across the cooler when the valve is open. The LP EGR valve uses vacuum that is modulated by a pressure converter under the intake manifold to actuate the valve. Pretty common to have a leaking vacuum hose or dead pressure converter (vacuum control valve).

ISTA+ has test functions to exercise the EGR valves.