I recently updated my application from version 4.7 to 4.9. After the update my web map fails to load any feature layers and I get the following errors in the console:
ERROR TypeError: Failed to execute 'shaderSource' on 'WebGLRenderingContext': parameter 1 is not of type 'WebGLShader'.
at a._loadShader (js.arcgis.com/4.9/esri/views/2d/layers/features/tileRenderers/SymbolTileRenderer.js:211)
Oddly, the map will load successfully, without error, about 1 out of every 10 times (with no code changes).
Switching back to the 4.7 version and the map loads fine with no errors.
I can post code if necessary (large application), but hoping someone has seen this issue and has a general solution.