When uploading a credential of kind "Certificate", after selecting the "Certificate" option from the "Kind" dropdown and then clicking the "Upload PKCS#12 certificate" radio button, the Jenkins UI displays an "Oops - Not Found" error. See pkcs12-before-browse.png

Browsing and selecting a certificate results in an error: "An internal error occurred during form field validation (HTTP 404). Please reload the page and if the problem persists, ask the administrator for help." See pkcs12-after-browse.png

In the browser inspector, I can see one HTTP POST request with a 404 status code to the URL https://<JENKINS_URL>/manage/credentials/store/system/domain/_/'/descriptorByName/com.cloudbees.plugins.credentials.impl.CertificateCredentialsImpl$UploadedKeyStoreSource/checkUploadedKeystore.

This issue is a blocker, as it blocks users from adding PKCS#12-type certificates to the credentials store.