Identity element vs probes

Hello. Can anybody help me with the difference between probes and identity
element? I have a use case where I have an appsrc acting as a file source
-> identity -> sink. The identity element is not manipulating the incoming
buffers, but it is a mechanism to report heartbeats or health of the
pipeline to suggest there is data flowing from source to sink. But, I am
noticing that despite having media flow, the identity element's callback
does not get triggered at times and it is hard to debug why this could be
happening. So now I am looking into probes as a mechanism to report
heartbeats periodically, but I do not quite understand the underlying
difference between the 2 and what I should use for this use case. Anybody
who has implemented a similar functionality before?

Regards,
Divya