I know it sounds crazy but switching your date and time update from automatic to manual can cause this problem. Some time back I noticed my clock was wrong by an hour, so I switched off automatic date and time update, thinking it was connecting to the wrong time server or something. For the next two months I had a problem with opening the Alexa app trying everything to fix it - clearing storage,cache, uninstalling, force stopping, switching on/off wi-fi etc. etc. until I switched automatic time update back on. As soon as I did, Alexa went into it's update routine for the latest version and everything was OK again.