Hi and welcome to OESF (and the somewhat wonky environment of the Cosmo).
While this, on it's own, likely isn't the answer you're looking for, I don't have that particular problem with my Cosmo, which suggests it should be avoidable on your device too.
I rarely reboot, lest I have to (my keyboard has a tendency to stop working a few times per month) so uptime well over a week isn't unusual for me. If what you describe was a general Cosmo or Android problem, I should reasonably have run into it too.
I have left DuraSpeed on, and switched on the toggles for the apps I need to keep running in the background. For me, that's things like Skype, Spotify, an app showing the date in the status bar (why Android can't do that is beyond me). I have also left the "Intelligent power saving standby" and the battery manager on, mostly since they haven't caused me noticeable issues thus far. According to developer options my average RAM usage hovers around 40%. My Cosmo runs Android only and isn't rooted.
In other words, I've done nothing in particular, and I don't have this issue. By itself, that might be less than useful to you. However, if more users chimes in with their settings and experiences, perhaps we can, together, find some kind of pattern to this. So, is anybody else experiencing this or not, and what are your settings?