If going to do no new testing; When cold, it could be an inaccurate fuel pressure report to the ECU by the G410/thrust sensor on the hpfp. Perhpas it has only just begun to fail in some way. Temps affect the pressure as you know, and if cold the pressure would be lower. But if the G410 is reporting a higher pressure...then that could be causing it to drop actual pressure leaving the high pressure to suffer. Peeking at the PSIG(gauge) in the low side may help determine if the G410 is accurate or not. Or, simply try another G410 to see. If it makes no difference...remove it, reinstall the current, and hang on to the new G410 until needed.