Since the latest MSFS 2020 major update (XI Canada) and SDK 0.19.3, there have been major issues with changing materials for Aprons and Taxiways. Whenever, the default material is changed, no new material is displayed but a chequered texture (see enclosed image).
A red error message can be read from the Material Inspector : "Material is not from selected assets group and can't be changed. Save, Delete, Reset and Apply locked"
The new Nvidia driver update (517.48) didn't solve anything.
Thank you for your assistance