Starting with Substance Painter 2018.3.0 the following kind of artifacts can appear in the viewport :
These artifacts are related to issues with Nvidia GPU Drivers.
To avoid the artifacts the Sparse Virtual Textures hardware support needs to be deactivated.
The GeForce Drivers 440.97 have now fixed this issue. We recommended to update to these drivers and to keep the SVT enabled to get good performances.
New drivers are available on Nvidia website: https://www.nvidia.com/Download/index.aspx
Disabling the Sparse Virtual Textures Hardware acceleration
1 - Start Substance Painter and open the Settings
Open the main Settings via Edit > Settings.
2 - Find the section named "Sparse Virtual Textures"
Inside the "General" section, scroll down and find the sub-section named "Sparse Virtual Textures"
3 - Uncheck the setting
Disable the "Hardware support acceleration" setting by unchecking it.
4 - Validate and restart Substance Painter
Validate the change by clicking on the "OK" button.
Restart Substance Painter by clicking on the "Yes" button to apply the change.