When you say "noticed that emails are downloading slower and slower or sometimes not at all" --
-- do you mean the app is slow at syncing mail, when it's talking to the mail server?
I assume the tablet's connection type is WiFi, correct?
Are you seeing this is one account only or several?
If you only have one mail account in Aqua, do you have any others you could add, for comparison?
Ultimately, the best option is to capture the issue in the app's debug log (see my signature, below, for a link on how to do that). You will need to enable "raw session data" in log settings for it to be useful.