I have in-sim messages turned on so I can definitely see whenever it rebuilds the cache.
Please re-read my post again, especially the part which explains there are two caches ( airport and objects ), and there's no message telling you the object cache is ready and, if you try to start GSX before it is, it might not work.
That's why I asked, on an airport with GSX jetways, to wait for the jetways to appear, before starting GSX. Do this after starting clean, meaning after an FSDT Live Update.
Instead of running the Live Update, try to just remove this folder:
C:\ProgramData\Virtuali\Couatl
If you notice the effect is the same as running the Live Update ( fixing the start for one session ), at least we know IT IS something related to the creation of the two caches so, be sure you try to wait a bit for the jetways, so we would know if the problem is in fact trying to start GSX when the object cache is still rebuilding ( which, again, doesn't have a prompt, we are planning to add it )