When we first bought our previous van, our first two nights had no trouble, then moving on to a second site, we had the "connection error". I wont bore you with the whole dealer argument, but when we finally got an engineer, he did the same thing, i.e. changing the PCB's etc and all to no avail. I had suggested that the connection error may be related to the data cable that runs from the panel to the boiler, and asked if there was a connection. I was told by Swift, Truma, and the dealer that it was all one cable and that there were no joints. However, the engineer decided the only thing left was to change the cable, and lo and behold, the supplied cable was about 50% of the required length. So, checking the cable for such a joint we found one in the cupboard, floor level just beyond the cooker. It was very similar to the sort of join you can put in telecoms cable, or the join to telephone cables together. In out case, the plastic lug/catch had broken off, so pushing the cable in was fine, but ifi it moved slightly, connection was lost. Madam may have disturbed it as it was the cupboard we ket the pillows in. Bit of insulation tape and we never had a problem again.
This is what you are looking for in the caravan
https://www.amazon.co.uk/Truma-Control-Panel-Extension-Cable/dp/B07FS7KSBR