I see that an SDK update is available.
Do you think this is SDK related?
Otherwise there are a few other posts like
non-English Windows User - Unable to start new flight, Permanent stuck on loading screen - #37 by ShinyChariot114,
Stuck on loading into flight with progress bar filled,
Stuck on final loading when bing data world graphics is turned on.
You can find them in the #bugs-and-issues:performance category.