I had that problem (intermittent, random logouts) as well. Strangely, I've been planning our next trip (we're within 180 days so I've been getting into super planner-mode with dining, extra excursions, etc.) and I've actually been able to stay logged in for a week or two without getting logged out.
In any case, I highly recommend a password management service/app. Not only for password safety in general, but it sure makes re-logging into any app/website easy. I use (and recommend) LastPass, but there are others. With LastPass on my phone (Samsung S7 edge) whenever an app asks me to log in, I swipe down, press "LastPass Fill Helper" and using my fingerprint, it automatically logs me in. Saves having to remember passwords and/or trying to type while walking, dealing with sun glare, etc.