Got two sets last week and had all the problems with mine as mentioned here derailments etc. Have cured the problems with the 3 coaches bogies catching around the bends which are quite decent, clicking bodies etc.
Have slackened the screws on the coupling drawbar , not too much just enough so they dont twist and put power lube on the v shape groove and also the large plastic eye under the screw and made sure they dont jam at all by waggling and retighten ar slackened screw slightly in very small increments reqd.
Result no more bogies fouling on coaches and derailing.
But found and interesting thing abought the bogies, pull of the rear dummy bogie and put it on a coach, non pickup bogie , and found impossible to foul the coach body but the coupling is the real problem .