Backup to Azure

I am backing up to a Azure blog storage. It is a single system backing up, and another one forgetting once and pruning once a month.

Recently I run a check and found a lot of:
pack f9d5d768: not referenced in any index
(which is due to forget, so there shouldn’t be a problem) but also

...
error for tree 5ed0936b:
  tree 5ed0936b: file "breton.dict" blob 0 size could not be found
  tree 5ed0936b: file "breton.info" blob 0 size could not be found
  tree 5ed0936b: file "disambiguation.xml" blob 0 size could not be found
  tree 5ed0936b, blob 54ffdfa5: not found in index
  tree 5ed0936b, blob 133f320f: not found in index
  tree 5ed0936b, blob a301998a: not found in index
...
Fatal: repository contains errors

My first concern is how to fix it, and how to avoid it happening again.
The container is configured as:

Performance/Access tier: Standard/Cool
Replication: Locally-redundant storage (LRS)
Account kind: StorageV2 (general purpose v2)

Thanks