Looking for an answer to a specific case within Exchange Hybrid Free/Busy sharing across two org.

Hello,

At first let me say that we are really exhausted by finding some real answers for our problem. We tried Microsoft Official support which leads us nowhere, we read official and un-official documentations but the answer is nowhere to find. We have this problem for months and we can't find any reliable source of information to answer our questions.

The context:

• We have two separate organizations. By separate organization I mean separate AD DS, separate M365 and MS Entra ID, separate physical place, separate management etc..
• The setup within these two organizations:
  • Organization A:
    • AD DS, ADFS, AAD Connect, M365 (MS Entra ID), Exchange Online (only)
    • All hybrid users in this organization have their active mailboxes in Exchange Online only. Non-hybrid users doesn't have any mailbox.
    • THERE IS NO EXCHANGE ON-PREMISE SERVER! ALL EXCHANGE ON-PREMISE SERVERS ARE DEALLOCATED AND DELETED!
    • Exchange Online has sharing configured against Organization B Exchange On-premise server and Exchange Online server and it's configured correctly.
  • Organization B:
    • AD DS, ADFS , AAD Connect, M365 (MS Entra ID), Exchange Hybrid (Exchange On-premise server and Exchange Online.
    • Users in this organization have their mailboxes in Exchange On-prem or in Exchange Online (depends on the situation).
    • Their autodiscover DNS is pointing to their Exchange On-premise server.

Now the problem:
We as Organization A are unable to retrieve Free/Busy status of calendars of users in Organization B WHEN the users in Organization B have their mailbox located in Exchange Online.
Let's put it another way:
I as an user from Organization A can retrieve user's free/busy status in Organization B when the user's mailbox is located on Exchange on-premise. However, when the user is migrated to Exchange Online within the Exchange Hybrid setup in the Organization B I as the user from Organization A can no longer retrieve the calendar free/busy status from that user from Organization B.

The questions:
1. Why the free/busy status retrieval doesn't work when an user in Organization A is retrieving it from an user in Organization B while the user's mailbox of Organization B is located in Exchange Online within the Exchange Hybrid setup in Organization B?

We will be very thankful for any information to this case.