Long Delay in Fax Delivery

There is often a long delay (1-2 hours) after we submit a Fax API request, before RingCentral first attempts to deliver the fax. During this time, our outgoing fax messages just sit in the outbox of the extension that we're sending as. Anecdotally, this seems to happen more in the afternoon (Eastern USA time). I called the main RC support line, they told me that they cannot help and I need to contact developer support (which I did and waiting for a response).

I suspect this is not strictly an API issue, but I'm wondering if any other API users have experienced this. It's pretty important as our clients are not receiving time-sensitive messages in a timely manner. I wonder if RC is somehow de-prioritizing delivery of our messages, as we do send thousands of faxes per month using the API. This said, we are careful to not exceed the API rate limits.

Has anyone else had similar problems?