Possible PBO management issue?
movit has this note in resource_pool:
// Memory management (only relevant if you use multiple contexts): Some objects,
// like FBOs, are not shareable across contexts, and can only be deleted from
// the context they were created in. Thus, you will need to tell the
// ResourcePool explicitly if you delete a context, or they will leak (and the
// ResourcePool destructor will assert-fail). See clean_context().
glsl_manager manages a PBO (see get_pbo)