To expand - we do AAD sync’d from on-prem, SAML, MFA (conditional access), through ADC and into Citrix using FAS. We have no problems with password changes/resets done in AAD being written back to on-prem. It takes just a few seconds for the write-back to happen. Sounds like something is amiss, check sspr settings and write back, and check AADConnect is up to date and configured appropriately, you need to give permissions to the AAD Connect service account to be able to reset user passwords in on-prem AD (all domains in forest).