Adding contributions through the bot when existing contributions do not validate lead to "trouble processing request"

[unode]

⚠️ This is a guess diagnostic and would appreciate input from maintainers of the all-contributions bot.

Describe the bug

Adding contributions through @all-contributions fails when existing contributions include authors not listed as committers.

To Reproduce
Steps to reproduce the behavior:

1. Using the CLI, add a code contribution for a GitHub user that hasn't contributed to the history of the repository
2. Push to GitHub
3. Try to use @all-contributions please add ... on that repository
4. The We had trouble processing your request error is likely to appear

Expected behavior
A clearer error message with some diagnostic information would be appreciated but in this case, not failing would be reasonable as well.
Consistency between CLI and bot behavior.

Screenshots

See this issue where the request was made and the subsequent failure message.

At the same time, using the CLI, the output of all-contributors check was:

$ yarn all-contributors check
yarn run v1.22.19
$ (...)/firefox_decrypt/node_modules/.bin/all-contributors check
Unknown contributors found in .all-contributorsrc:
tennox, Anthropohedron, alejandro-amo, yermulnik

but adding credit to rma-x locally worked fine.

Additional context

While no co-authored commit exists for some of these users, they have been acknowledged in commit messages

If my diagnostic is correct, it would be useful to have a mechanism to override this type of validation.
In this case credit is due but the bot can't validate that code contributions exist if a commit wasn't made.
Would having a skipCheck or adequately named flag at the user level be fitting?

I also couldn't find much explanation for the "trouble processing request" error. Would this be a candidate for a FAQ?

[KomoriDev]

I didn't set commitConvention, but I still encountered the same problem