Hybrid 2010 and Office 365 Message

Hello

We have Exchange 2010 and Office 365 set up in full hybrid mode.

I have migrated some mailboxes over and mail flows as expected.

Some of the mailboxes had a non default Receiving Message Size set while they were still on premises. But few migrated mailboxes have the old limit that is overriding any limit set in Exchange Online.

When looking at the Remote User Mailbox in the Exchange 2010 interface I can see the Maximum Message Size under the Mail flow Settings tab but it is greyed out and hidden behind a padlock indicating we can't modify it.

Anyone can help on how we can change these limits so that the migrated mailboxes respect the Exchange Online size limits?

Thanks