When disabling Cached Exchange Mode always remember to navigate to the mailbox’s OST file and either rename or remove the file from that location. This needs to be done because for some reason Outlook will not switch completely to “Online” mode if it finds the OST file that it was previously using on that profile. I haven’t confirmed this with Microsoft and I am not sure why this happens, but my best guess is that Outlook just starts using the settings saved in the profile since the last time it was closed and maybe it doesn’t refresh its “Should I be on cached exchange mode or not?” until it can’t find the OST.
Again, no guarantees here, just a tip that has saved me headaches for a few years.