Ok, I will explain wifi repeaters(the only way to increase wifi speed unless you are wired) and external expansion hard drives(only buy at stores like BestBuy since online buying external hard drives may not be expansion). When you get an external hard drive make sure the USB cable is blue tip part that connects to ps4 and another end(3.0) connects to external hard drives. Ps4 will recognize the external hard drive as expansion storage( if not then bring hard drive back and ask for Expansion external hard drive).
Your games will load quicker when transferred to the external hard drive. The regular ps4 internal hard drives will be slow for black desert including the frames.
I have a regular ps4(not slim or pro) and had the same slow problem. When I got the Seagate external hard drive(2 TB) and transferred to it. The game loaded much faster and less invisible walls and framed increased and I don't have a wifi repeater since my ps4 is directly connected to the modem through Lan set up.
Now if you know the above info and still have a problem you can google SATA external hard drives 3.1 USB cable. The 3.1 USB cable transfers 10gb of data transfer. It's expensive and 3.0 ones are ok for me.
Wifi repeaters increase wifi speed up to 300mbps(for a $29.00 one on Amazon may be cheaper for you) and range close to or more of 600sqft and can work your slow internet speed(even 30 mbps speeds). You can use more then one wifi repeater(when getting another make sure to get same type or there could be electronic communication complications).
Hope this helps.