This is pretty old (already been happening in 2019) and definitely unrelated to the ECO pack, which I don't own. My sims are always putting the Slablet on the floor, even though there's always room on nearby furniture, or in their inventory. I'd understand if this would happen with Sims who have the Slob trait, but in general? Definitely not. I constantly have to put it back in sims' inventories or on furniture, which is becoming tedious.
I do not own Eco, and ftm this is still here after 1.68.
I'm really tired of searching for slablets through all the house. Because you never know where the sim have left it, as I do not watch every second of their actions...
It's not only tablets, though I have a toddler tablet in the sand of my wellness center, which I can't move anymore (sigh). What really bothers me is their violins and guitars. I play a lot of musicians who have their instrument with them and around 50% of the time they place it wherever they are when they stop playing. One of my self made guitars ended up on public ground next to some beach. A very valuable violin also on public ground. And if one of my sims needs his guitar I find his inventory empty.