If a non-admin user opens the dialog to delete a service account, and does nothing, the modal dialog will disappear. Subsequent attempts to open the same modal will fail. See the first 10 seconds of this video:

sa-non-admin-behavior.webm

HTTP 404s are logged, but the service account is not deleted, and the HTTP 404s do not occur because of the service account being deleted.

An admin user within the same account/org can successfully delete service accounts, so it's unlikely there's some weird issue with this specific account. Issue produced with the following users:

• service_accounts_non_admin
• service_accounts_admin