Trusted Signing - Identity Validation fails with Name mismatch JORGEN SPIEGEL despite correct name everywhere

I'm setting up an Artifact Signing / Trusted Signing account (organization "JS Consulting", public identity type, Austria). The organization identity validation repeatedly fails with:

Error: Name mismatch. Please go back to Artifact Signing to update your contact details. Input: JORGEN SPIEGEL

My correct legal name is Juergen Spiegel (with umlaut ue). This is confirmed correct in my Microsoft account profile ("Vollstaendiger Name: Juergen Spiegel") and in my Microsoft Entra ID directory entry.

I entered "Juergen"/"Spiegel" (with umlaut) explicitly as First/Last name in the Trusted Signing organization vetting form on a fresh submission (Identity Verification ID: 0cc8846a-6b00-4db1-b251-9622c97f0183, Subscription: cbfaa84f-9a1d-4561-b60b-dc39dd3984ce), but the validation failed again with the identical error text "JORGEN SPIEGEL" (no umlaut). This suggests the umlaut is being dropped or mistransliterated somewhere in Microsoft's backend identity validation process, not an input error on my side.

Has anyone encountered this with non-ASCII characters (umlauts) in Trusted Signing identity validation? Is there a way to get this manually corrected or reviewed?