This was answered in another thread. We removed the remember me feature per a review from security experts who said such a feature can lead to member's accounts being hacked. The report mentioned it is not a good feature to have these days for any site. As such, we removed it for better security. 

Per the security experts who did the audit a few years ago, it isn't something we would add back but there may be a plugin if that's how you want to have your site. Due to risks, we aren't willing to take the risk as it would be a huge liability to put something the security experts said not to have. 

There was a post before that had tips to edit the core to add it. I'll see if I can find it.

I couldn't find the post but I searched the store, https://community.socialengine.com/classifieds?category=21 and there are a lot of log in plugins. It could be that one of those would do what you want. If not, if you'll contact one of those experts they can probably do this for you. I believe the free mobile apps allow an easy login via the mobile app as well.