The domain troubleshooting guide can help with most custom domain configuration issues. You might be able to use that guide to solve it before a human is available to help you. Then you can come back here and share the answer for bonus points.

https://vercel.com/docs/projects/domains/troubleshooting

You can also use v0 to narrow down the possibilities.

Partially solved, details below for retrospect.

After finagling around, I was able to narrow down to the issue being Cloudflare's fault. On Cloudflare dashboard, I ran a trace against the endpoint https://aaanh.com/hero-movie.mp4 and saw that it was blocked by the Super Bot Fight ruleset on Cloudflare.

With the proxy still enabled, I disabled the all 3 bot prevention rules on the dashoard (screenshot) along with enabling Development mode which bypasses any cache.

And this screenshot shows the trace after disabling the bot rules.

Finally, I purged all cache on Cloudflare again. After which, I purged the browser (client) cache to be sure and the video has finally been able to load again.

Then I disabled the Development mode on Cloudflare and the issue resurfaces again intermittenly. 😭

In case it's helpful, we actually just rolled out our Bot ID detection SDK which will give you fine grained control over which bots you block or remove directly within Vercel

https://vercel.com/docs/botid

vercel.com

BotID

Protect your applications from automated attacks with intelligent bot detection and verification, powered by Kasada.

In general, layering two firewalls (Cloudflare and Vercel) will cause problems because each acts as either a source or destination proxy that prevents traffic from being properly triaged, so unless you have a corporate requirement to use CF's firewall specifically then you may be able to use Vercel's Firewall (WAF, DDoS protection, and now Bot Identification too)

https://vercel.com/docs/vercel-firewall

Hello Jacob,

Thank you for the suggestions and insights. The more I test the setup (turning combinations of configs off and on), the more I'm convinced it's Cloudflare that's blocking the request for the video asset from even hitting Vercel 🥲 (Screenshot of the trace on CF's side)

I guess it's something that was changed on how CF handles bot protection without much notice since the error only started happening recently. I don't think it's the direct consequence of sandwiching CF and Vercel firewalls, but I'm a bit annoyed at CF now, so I'll switch to only Vercel firewall for the time being.

Although my personal site doesn't have the corpo requirements to mandate CF proxy, my setup more or less reflects the configurations I do at work, so this is something we might need to discuss more internally

Edit: I managed to bypass CF Super Bot Fight Mode, which is only manageable with a Pro and up plan, by having a custom WAF rule on CF to skip evaluating rules including the Super Bot Fight specifically for that video asset's URI.