Backup failed with permission denied

I’ve been using Discourse successfully for a while now, but backups have all of a sudden stopped working.

Relevant line from the log is below. Not sure what would have caused this permission error to start happening from out of the blue. I was going to start mucking around, but thought I’d ask here if there was an easy known fix.

...
 Making sure archive does not already exist...
[2019-04-10 03:44:45] Creating empty archive...
[2019-04-10 03:44:45] EXCEPTION: /var/www/discourse/lib/backup_restore/backuper.rb:225:in `create_archive': 
tar: /var/www/discourse/public/backups/default/xxxx-forum-2019-04-10-034440-v20190306154335.tar: 
Cannot open: Permission denied
tar: Error is not recoverable: exiting now

저도 같은 예외가 발생하고 있습니다. 해결 방법을 찾으셨나요?

아마 며칠 동안 더 조사할 시간이 없을 것 같습니다.

개인 정보를 ####로 편집한 예외 메시지는 다음과 같습니다:

[2020-12-07 22:43:42] EXCEPTION: lib/discourse.rb:92:in `exec': tar: /var/www/discourse/public/backups/default/XXXX-XXXX-2020-12-07-224327-v20201116132948.tar: Cannot open: Permission denied
tar: Error is not recoverable: exiting now

이 개인 사이트는 다음 환경에서 실행 중입니다:
Discourse 2.7.0.beta1
Ubuntu 20.04
Digital Ocean

저도 동일한 오류가 발생했는데, 해결책을 찾으셨나요?