I have ran into similar problems using my S10 with companys EAS account. Email app simply wont sync and I would not receive emails when they arrive. I found out, that O365 bloks the client app from accessing the mailbox if the app reaches a certain sync request treshold. Long story short, with the recent Samsung Email app update (ver 6.1.01.0) sync problems seem to be resolved. App syncs in the backgroud like it should and I get a notification for all the mails.
I also have had this issue. My IT department has also verified everything on their end. My network guy and myself began digging into this issue. Which is all over the internet and no one provides answers. My phone has been working well so far. The solution came in the form of putting together multiple threads. The phones Samsung/google built-in email app needs to be updated, it apparently interferes with other email apps even though I never used it. Then it is like a worm it has all your accounts already established in there. I did not have any emails in it but it was ready to go. So I deleted all my accounts from it, closed it and my Outlook app has been working fine since then. I hope this helps and I am keeping my fingers crossed because it might just be a band-aid but so far so good.
All of these issues are Exchange Online issues, you need to validate the correct configuration on exchange online security wise, and so on. Then remove and re-add the mail address to your phones.