I too have had major issues with the Alexa app for quite a while. It is very very slow. This is not an issue with Wi-Fi or my network as 1) the many other devices and apps on my network don't have the same issue and 2) I have exactly the same problems with the Alexa app when away from home and using cellular data.
Usually, when the app opens, I'm shown the menu icon (three lines) and the title 'Home', but the content of the Home page takes around two minutes to load.
Apart from being slow, I find that I am able to open the menu, but then unable to select any menu items. Touching them does nothing. If I wait another 30 seconds or a minute, I can often then select an item, but this situation is unworkable.
If I am able to select a menu item, I'm often not able to perform actions in that section. For example, deleting items from the Shopping List.
Yes, I am very familiar with the Echo. I have an Echo, one Dot and one Tap and have RTFM, but thanks Mike for your stellar advice.