Hub losing a typed email sounds like a Hub bug as you say.
Your other issues I've only seen in low end Android phones that have insufficient RAM.
Both my Note 4 and S7 Edge keep things in memory long after I have used them, I often open links from FB or Twitter to Browser eg. news articles, I will have +10 tabs open in the browser weekly and another 10-20 in Opera Mini, and they usually stay open with no reload, unless I setup my phone to App Power Save, in which case it will pause and reload some apps if required (this is what caused the whole S6, S6 Edge and Note5 Multitasking debacle last year).
The beauty in Android really is in creating your own experience. Today my S7 Edge is a Multitasking beast running multiple productivity apps from Microsoft, Google, Samsung (S Note and S Planner), along with Social Media, and entertainment (Music, Netflix, Games etc...), BUT if tomorrow I do not require these apps to stay in memory I throw them into 'Always Power Saving', e.g. on a day where I am on holiday and only require the Camera and Social Media apps to be priority.
There are also then apps that are built to pause and reload no matter how much RAM is available and no matter what is priority, so this is also down to developers and how they built the app.
My bank's app is built to default to the login screen if you leave it in the background for more than around 15seconds, for example, as a safety measure.