I loaded a flight in EGLL and had to leave the PC for a few minutes. When I returned, all jetbridges were available. It could be that I didn't wait long enough for the airport cache to reload when the jet bridges didn't load.
In general, you shouldn't always recreate the airport cache manually.
The only case in which you must do that, is when a 3rd party scenery that comes with a configuration utility that switches between different AFCAD for the same airport using file *renaming* and that cannot always detected by GSX automatically but, in normal use, rebuilding the cache is not required.
And, to minimize the airport cache rebuild time, add the simulator own folder ( and if you have sceneries installed outside of it, add their own folders too ) to the antivirus Exclusion list. This can make for a huge difference in the cache rebuild time, when needed.