eM Client is cutting out about half the incoming mail.
Could be then you have enabled Inbox Categories where “unless you disable them on install”, all your incoming email is sorted into Categories in V10, where different accounts such as a eg: Gmail account have Inbox tabs Primary, Promotions, Social, Updates. Outlook accounts have a Primary & Other Category tab.
So if you see a “Primary” tab above your email, “look to the right of that” and see if you have more tabs to click on where I suspect your missing mail is.
If you then find the missing mail in another category tab, then you can either “drag it back” to the Primary Inbox tab or drag it to any other Category tab, or you can “right click on the email subject” and select the category you want it to go via the dropdown menu. Either way you will get a prompt appear to confirm for future emails
If you only want “some categories enabled” or want to “disable / hide categories completely” and just have the one main Inbox, then see my post in the link below.
https://forum.emclient.com/t/my-inbox-is-divided/106871/2
Also see eM Client online documentation on Categories.
https://www.emclient.com/webdocumentation/en/10.0/emclient/default.htm#E-mail/Inbox%20Categories.htm