The ping on your IMAP server is fine so I suspect the problem is at your end.
Hiding messages marked for deletion will provide a temporary fix but isn't curing the problem - your inbox will still gradually fill up with messages, even though you can't see them, slowing matters down even further.
To sort this out further would require some hands-on with your PC. If you want me to try that, and of course I realise you may not want to take that risk, you can install an excellent piece of free software called TeamViewer (www.teamviewer.com
). That would allow me to control your PC remotely while you watch. We could then set up a convenient time to have a go at finding a proper fix. Let me know if you want to try that.