Getting InvalidSsmlException For Valid SSML (Neural voices only)

Here is the SSML in question:

<speak><prosody rate="100%" pitch="-21%">India's massive COVID surge puzzles scientists</prosody></speak>

Not that if I remove the pitch attribute it does not fail. Also, the same SSML works fine for Standard voices. Is there a bug? The same SSML worked fine previously for Neural voices but stopped working at some point recently. Any help is appreciated.

Edited by: bretwilliam on May 2, 2021 10:26 AM

Edited by: bretwilliam on May 2, 2021 10:27 AM