First, you haven't updated, because your version is still 3.4.3. However, that is not the point about that error, assuming with "error", you mean this message:
"The loaded flight plan from LFTW doesn't match the one on SimBrief, from EGSS to LFTW"
This is not a GSX error, everything is fine, but if you are doing a turnaround, you are not supposed to click the Simbrief reload button after you landed, you should do that only AFTER you filed a plan on Simbrief with the return flight.
