Alright, I seem to have figured out some voodoo that works on my end.
- Run the Docker image as normal
- Keep trying to open docs on Nextcloud…
- Click “OK” on “Well, this is embarrassing, we cannot connect to your document. Please try again.”
- Click “OK” on “Service is unavailable. Please try again later and report to your administrator if the issue persists.”
- Keeping going back to step 3 until you finally get “Failed to load the document. Please ensure the file type is supported and not corrupted, and try again.”
- Click “OK” and exit to Files.
- Restart Docker itself (the service, not just the image).
- Profit.
Why this works, I have no idea but it has worked three times in a row for me. I hope it’ll help someone else and, ultimately, I hope it provides a clue needed to address the problem.
It’s not a real “Solution” but I’ll mark this as solved for now.