I'm really not sure how to describe this issue succintly, so I'll give the long version:
We have an entity "relationship" which contains 3 relevant lookup fields.
Related Account -> Links to Account
Related Contact -> Links to a contact
Related User -> Links to a System User.
In the old CRM 2016 on-prem enviornment, if you were to update the account on the contact record, the "relationship" record's account would also change. However, when we moved to crm Online, that behavior no longer persists. I'm not able to ask the original developers/configurers so I'm not sure where to look. I've reviewed the cascade settings and they seem to be the same, and there arent any busines rules or workflows that modify these fields (also not even sure how they would do it).