Hello Daniel Gellard,
Thanks for your question.
This could be due to minimum age.
If you have a minimum password age and have recently changed the password within that window of time, you're not able to change the password again until it reaches the specified age in your domain. For testing purposes, the minimum age should be set to 0.
See: https://zcusa.951200.xyz/en-us/entra/identity/authentication/troubleshoot-sspr-writeback
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Regards,
Abiola