iFrame PDF Forbidden on Live Site

I am currently experiencing an issue on my site where my embedded PDF will not display on the published site at the moment and only displays ‘Forbidden.’ This issue happens periodically with no obvious triggers. This issue was previously discussed here:

Is there a solution for this? It’s very frustrating. Here’s the selection of PDFs that are currently forbidden…choose any one:
https://www.rcmcollection.com/Archives