Webasto Auxiliary Heating–> Flammation

Hello people Have a Webasto heater with HTM 100. It works “in general” quite well. But more and more often it doesn’t run perfectly in the morning. The heater goes off briefly, then the fuel pump, which is installed near the tank, starts to clack loudly, about 3-4 times as loud as normal. That’s what it is, then the heater goes off again and stores the error message Flammababbruch. I was also at the Bosch service, but these find nothing, because if I go to the Serv I’ve already asked Webasto via e-mail, but they only write back with the answer, the responsible Bosch service may get in touch with them. But they don’t find anything. The mistake doesn’t happen regularly, can it happen three times a week, then the heating runs again for a whole week without any disruption. Do you know this mistake?