Workaround that does not fix the real issue. The bug is caused by glBufferData inside DRW_instance_buffer_finish > GPU_vertbuf_use but only after the selection code which resets the number of items in idatalist->pool_buffers. I don't understand why this is happening as the vbo ids are all valid and no error is reported. What is even more strange, is that it affects another vbo which has no connection with the ones in DRW_instance_buffer_finish.