Imagery stops loading when changing terrain in request render mode

Easiest way to reproduce

• Zoom in close to the ground and hit the Disable terrain button until the imagery stops loading in (usually 2-5 clicks)
• Hit the Enable terrain button
• Now the imagery never loads in, even after the camera moves

I wasn’t able to reproduce this when requestRenderMode: false, so it seems to be related to those changes. It seems like it might be related to changing the terrain before all imagery tiles are loaded, but I’m not sure.

var viewer = new Cesium.Viewer('cesiumContainer', {
    requestRenderMode : true,
    animation: false,
    timeline: false
});

var cesiumTerrainProviderMeshes = new Cesium.CesiumTerrainProvider({
    url : 'https://assets.agi.com/stk-terrain/v1/tilesets/world/tiles',
    requestWaterMask : true,
    requestVertexNormals : true
});
viewer.terrainProvider = cesiumTerrainProviderMeshes;

Sandcastle.addToolbarButton('Enable terrain', function() {
    viewer.terrainProvider = new Cesium.CesiumTerrainProvider({
        url : 'https://assets.agi.com/stk-terrain/v1/tilesets/world/tiles',
        requestWaterMask : true,
        requestVertexNormals : true
    });
    viewer.scene.requestRender();
});

Sandcastle.addToolbarButton('Disable terrain', function() {
    viewer.terrainProvider = new Cesium.EllipsoidTerrainProvider();
    viewer.scene.requestRender();
});

[hpinkos]

Well, I actually can’t reproduce this anymore. @mramato reopen this if you still see it

[hpinkos]

Probably not going to have a chance to look at this for the July release, but I’ll have a reproducible example ASAP so we can fix this for the August release