Exchange Web Services FindItems finds less items then get-mailboxfolderstatistics

Hi,

I've created a script, that detects email in outbox and then it uses EWS to move mail to sent items.

But in most cases get-mailboxfolderstatistics finds more mail (usualy 1-2 more), than EWS.
I thought that it's because of hidden/corrupted items, but I can access that missing email using Outlook client without any problem.

Do you have any idea why it happens?

I have tried newest EWS API, but it does not help.

Thanks

M.