Can you try:
- Setting your “layer blend” node’s preview weights to 1.0 for the first layer and 0.01 for the others (this will force all layers to be included in the material).
- Pressing the “mobile stats” button on the right of the material editor toolbar.
This should try and compile the material for ES2 immediately and should tell you what the compile error is. If it compiles fine but is using all 8 samplers, then remember that landscape uses one extra for weights that the material editor might not know about.
I have asked about the number of textures used by lighting on mobile and it seems to be worse than I thought: It seems to be two for lighting and two for shadowing, 4 total. With the landscape requiring one for weights, that only leaves 3 textures for the user material under ES2 O.o
You can free one of the shadow texture samplers by going to Project Settings → Engine → Rendering → Mobile and disabling “Enable Combined Static and CSM Shadowing”.
I have been told we are working on ES3 support for an upcoming release, which would allow 16 textures. You would be able to use a feature level switch to remove some of the textures from your material for ES2-only devices (e.g. the normal maps) if you still need to support ES2-only devices, but the vast majority of modern mobile devices are capable of ES3.