SSL cert upload fails: Certificate invalid, or password is incorrect

Please provide us with the following information:

This issue is a: (mark with an x)

• bug report -> please search issues before submitting
• documentation issue or request
• regression (a behavior that used to work and stopped in a new release)

Issue description

Adding/uploading a SSL certificate to a containerapps environment fails, both in UI and CLI: azure.cli.core.azclierror.CLIInternalError: (InvalidCertificate) The certificate wildcard.stageargeo.no is invalid or password is incorrect.

I have tried both using a wildcard certificate and a non-wildcard SNI cert (as I suspected a regression of issue #229) but both fail on upload (UI shows successful validation, but error message after clicking the "Add" button. I have tried creating a bundle with and without password, but both variants fail. Recent comment in #229 also suggest more people having the same issue.

Steps to reproduce

1. Request Let's Encrypt certificate
2. openssl pkcs12 -export -out certbundle.pfx -inkey privkey.pem -in fullchain.pem to create cert bundle with full chain
3. az containerapp ssl upload --certificate-file certbundle.pfx --environment <aca-env-name> --hostname <hostname> --certificate-name <certname> -g <resourcegroupname> -n <appname>

Expected behavior [What you expected to happen.]
Successful add of certificate and option to map cert to container apps. I have previously been able to add a certificate bundle of the same type using the portal.

Actual behavior [What actually happened.]
Error message: The certificate is invalid or password is incorrect.

Screenshots
n/a

Additional context

Issue occurs both in the CLI and the Portal. Enabled debug and looked at http responses, but they give no further clues to as what is happening.