The coolant pressure test is obviously showing a coolant leak. The system should not lose pressure if there were no leaks. Since the leak is not external, it may be getting burned. Maybe the intake gaskets leaking again?
Did you check the exhaust for any traces of UV? Another thought is to repeat the pressure test, pull the EFI or ECU fuse to de-power the fuel injectors, and coil, and, after 10-15 minutes into the pressure test when the pressure drops, turn the engine over a few times. Then pull plugs and check for traces of UV dye on the spark plugs. If the leak is slow enough, it may be getting burned before it can drop into the crankcase.