The cache initialization operation (CacheInitOp) doesn't get updated after the first frame. This may only manifest if something else hasn't already triggered RegisterForCallbacks in ResourceManager.

We need to have ResourceManager Register for callbacks if there are initialization objects that get processed.

Quick Repro:

In CacheInitOp, change Update(..) to look like
int fakeFrameDelay = 0;
public void Update(float unscaledDeltaTime)
\{
#if ENABLE_CACHING
Debug.Log("we are waiting for init...");
fakeFrameDelay++;
if (fakeFrameDelay < 3)
return;
if (Caching.ready && m_UpdateRequired)
\{
m_UpdateRequired = false;

If you hack in calling resourceManager.RegisterForCallbacks when the InvokeExecute is called (or anywhere really) then it will work.