404 error when navigating with <Link> and v3_lazyRouteDiscovery on Vercel when using different runtimes per route

[styxlab]

Reproduction

1. Deploy the following git repo to Vercel:
   https://github.com/styxlab/lazy-route-discovery-link-404-on-vercel

2. Observe 404 error when clicking on "Navigate to About page and observe 404 error!" from index page.

Notes:

• Problem exists when switching from edge to node and vice versa
• v3_lazyRouteDiscovery must be enabled (bug vanishes when disabled)
• No problem when hitting the route directly.

System Info

remix 2.15.3, deployed to Vercel, node 22

Used Package Manager

npm

Expected Behavior

No 404 error when using

Actual Behavior

404 error when using and v3_lazyRouteDiscovery

[styxlab]

Similar to #10263 but different in that the runtimes play a role.

[styxlab]

Note: unlike #10494 and #10497 this error vanishes when v3_lazyRouteDiscovery: false only, i.e. singleFetch can be turned on.

[nicksrandall]

I've run into a similar issue and I added a reproduction here: remix-run/react-router#13117

Do you think your issue is related?

[styxlab]

I've run into a similar issue and I added a reproduction here: remix-run/react-router#13117

Do you think your issue is related?

Maybe the root cause is the same, but the symptoms are different in that this case only happens on Vercel infra when using different runtimes, whereas your issue can be reproduced in a local environment.