[BUG] Can't upload R2 incremental cache - recurring 503 Service Unavailable

[grabmateusz]

Describe the bug

We have a project, when with wrangler 4.42.2 and @opennextjs/cloudflare version: 1.11.0 we're able to bulk upload R2 incremental cache containing over 17k assets on regular basis.
When we update dependencies to wrangler 4.62.0 and @opennextjs/cloudflare 1.16.2 bulk upload of R2 incremental cache stops to work with recurring 503 Service Unavailable

Steps to reproduce

1. Create any project with hundreds of ISRed pages
2. Try to deploy it to CF

Expected behavior

Like with wrangler 4.42.2 and @opennextjs/cloudflare version: 1.11.0 - R2 is populated, worker is deployed

@opennextjs/cloudflare version

1.16.2

Wrangler version

4.62.0

next info output

Operating System:
  Platform: darwin
  Arch: arm64
  Version: Darwin Kernel Version 24.6.0: Mon Jul 14 11:30:29 PDT 2025; root:xnu-11417.140.69~1/RELEASE_ARM64_T6000
  Available memory (MB): 32768
  Available CPU cores: 10
Binaries:
  Node: 22.21.1
  npm: 10.9.4
  Yarn: 1.22.21
  pnpm: N/A
Relevant Packages:
  next: 15.5.10 // An outdated version detected (latest is 16.1.6), upgrade is highly recommended!
  eslint-config-next: 14.1.0
  react: 18.3.1
  react-dom: 18.3.1
  typescript: 5.3.3
Next.js Config:
  output: N/A
 ⚠ An outdated version detected (latest is 16.1.6), upgrade is highly recommended!
   Please try the latest canary version (`npm install next@canary`) to confirm the issue still exists before creating a new issue.
   Read more - https://nextjs.org/docs/messages/opening-an-issue

Additional context

We have a project, when with wrangler 4.42.2 and @opennextjs/cloudflare version: 1.11.0 we're able to bulk upload R2 incremental cache containing over 17k assets on regular basis. The logs looks as follows:

Populating R2 incremental cache...
Populating remote R2 incremental cache using batch upload...
Using batch upload with R2 credentials from environment variables
Successfully uploaded 17126 assets to R2 using batch upload

Now we would like to update to newest Wrangler and OpenNext, but it seems OpenNext changed the way of bulk uploading R2 cache, which is again error prone. In our logs we can see:

Resource location: remote 
Starting bulk upload of 16974 objects to bucket <bucket> using a concurrency of 50
Uploaded 0% (10 out of 16,974)
Uploaded 0% (20 out of 16,974)

and in the end:

Uploaded 21% (3,720 out of 16,974)
Uploaded 21% (3,730 out of 16,974)
▲ [WARNING] 🚧 `wrangler r2 bulk put` is an experimental command. Please report any issues to https://github.com/cloudflare/workers-sdk/issues/new/choose
▲ [WARNING] Processing wrangler.jsonc configuration:
    - Unexpected fields found in top-level field: ""
✘ [ERROR] Error uploading "<path>"
  Error: Failed to fetch <url>.fetch - 503: Service Unavailable);

In the end it is impossible to upload R2 incremental cache and in the end our deployment fails.

[vicb]

See this related PR

Feel free to chime in there and help to speed up the fix.

Thanks!

[grabmateusz]

@vicb I've given a try to mentioned PR. Current version does not work at all, I've spent some time to make it usable, but I've failed, neither do I support direction proposed in this PR.
Any reason functionality that was working fine and took a while to deliver was dropped:
#925
?

[grabmateusz]

@vicb I went through historical MRs, I've gotten familiar with your problem statement regarding rclone and I've submitted my proposal:
#1116
recovery of the #925 + fallback to current wrangler r2 bulk put.
For me this is most reasonable step to bring back ability to deploy projects with huge ISR cache + do not affect DX.
Additionally in my opinion proper step moving forward is to implement in wrangler r2 bulk put that will bypass Account Rate Limits.
Please get familiar with my proposal, looking forward to make it possible to use once again up-to-date opennextjs-cloudflare main branch :)