Spikes in Mesh.DrawVBO

As per request from @Dantus I created a separate post for this:

I created a simple test scene based on our game, and got spikes like these:



The frame right next to it:



As you can see this is for transparent geometry, but it happens also for the opaque geometry, and also in Mesh.DrawVBO.

Note: this is not in the editor, but in a webgl build

To rule out that this is a webgl only issue, these are the same spikes in a regular windows standalone build:



(look a the green highlighted spikes)

I made a bug report with case number 754393.

Anyone an idea what the cause could be? It is a very static scene, nothing fancy, runs fast, apart from the spikes.

Not unimportant: dynamic batching is off, so it's not that issue.