Got this problem too for all flights after updating to Level 2
Tried the solution provided, clearing the shaders cache, disable RTT, restore to default jetways, lowering texture quality. Nothing worked...
Tried a flight today at RJAA using PMDG 777-300ER, CPU usage was fine at around 20-30%. Didn't even tried to board passengers using GSX. After requesting push back, CPU usage ran off the roof. All cores at 100%. Airport texture became black, couldn't load aircraft texture. Tried refreshing Scenery Library, the game stuck at loading.
CPU: i7-4790 3.6GHz
Display Card: NVIDIA GeForce GTX 1060 3GB
*Same setting in the sim worked perfectly before Level 2.
**Tbh, I'm very disappointed, I can't even do any flights after Level 2