Not that I'm aware of.
What device specs? Android OS could be warning mull about its memory usage when it's moved to the background, causing the browser to quickly offload whatever it can to be kept partially in memory. Alternatively Android could just be killing mull's tab processes due to too many background apps running, only keeping mull's main executable cached for faster re-launch.
A restart might temporarily alleviate it if you've not restarted your device in a while, particularly if you still have this issue despite closing other apps