Steps to reproduce:
If you create backup storage, create a cluster and then later edit backup storage and change bucket name and/or credentials, it will do the backup in the old bucket/credentials or sometimes fail, but then on the subsequent try it will start using the new info.

$ k get psmdb-backup
NAME CLUSTER STORAGE DESTINATION TYPE STATUS COMPLETED AGE
backup-bbq mongodb-tio tomislav-backup-test s3://tomislav-backup-test/mongodb-tio/35751325-b3f1-4d22-8fd0-9e9a82703e28/2024-05-17T12:11:56Z logical ready 3s 38s
backup-ruf mongodb-tio tomislav-backup-test s3://tomislav-backup-test/mongodb-tio/35751325-b3f1-4d22-8fd0-9e9a82703e28/2024-05-17T12:06:46Z logical ready 5m14s 5m48s
cron-mongodb-tio-20240517114500-mczqv mongodb-tio tomislav-backup-test s3://tomislav-backup-test/mongodb-tio/35751325-b3f1-4d22-8fd0-9e9a82703e28/2024-05-17T11:45:21Z logical ready 26m 27m
cron-mongodb-tio-20240517115500-vbhsc mongodb-tio tomislav-backup-test s3://tomislav-backup-test/mongodb-tio/35751325-b3f1-4d22-8fd0-9e9a82703e28/2024-05-17T11:55:42Z logical ready 16m 17m

As you can see all backups are done to tomislav-backup-test bucket, but backup-bbq should have been done to tomislav-backup-test-binlogs bucket since I edited the backup storage and changed the bucket name.

So if you change credentials like I did later (I changed the account completely, bucket, and credentials)  the backup will fail, but then the next one will succeed.

apiVersion: psmdb.percona.com/v1
kind: PerconaServerMongoDBBackup
metadata:
creationTimestamp: "2024-05-17T12:35:16Z"
generation: 1
name: backup-jt2
namespace: test
ownerReferences:

• apiVersion: everest.percona.com/v1alpha1
  blockOwnerDeletion: true
  kind: DatabaseClusterBackup
  name: backup-jt2
  uid: cf84417d-69f6-48c9-9c11-071f584a3b7b
  resourceVersion: "145647"
  uid: 2faea974-6fc0-45c8-bce2-4ba35c8e3034
  spec:
  clusterName: mongodb-tio
  storageName: tomislav-backup-test
  status:
  destination: s3://tomislav-backup-test-binlogs/mongodb-tio/35751325-b3f1-4d22-8fd0-9e9a82703e28/2024-05-17T12:35:37Z
  error: "oplog: write data: upload to S3: AccessDenied: Access Denied\n\tstatus code:
  403, request id: xxx, host id: xxx."
  lastTransition: "2024-05-17T12:35:49Z"
  pbmName: "2024-05-17T12:35:37Z"
  pbmPod: mongodb-tio-rs0-2
  replsetNames:

• rs0
  s3:
  bucket: tomislav-backup-test-binlogs
  credentialsSecret: tomislav-backup-test
  endpointUrl:
  prefix: mongodb-tio/35751325-b3f1-4d22-8fd0-9e9a82703e28
  region: us-west-2
  serverSideEncryption: {}
  start: "2024-05-17T12:35:38Z"
  state: error
  storageName: tomislav-backup-test
  type: logical