DIAGNOSIS This is a common gripe with many Samsung smart TVs, including the QN85C. It's often a software handshake issue between the TV's network chip and your router, especially on congested 2.4GHz bands.
FIX First, forget your Wi-Fi network on the TV and re-enter the password. If that's temporary, dive into the network settings. Turn OFF the "Auto" for IP settings and manually set a static IP address for your TV in the same range as your router. This often stops the drops. Also, in your router settings, try assigning a reserved IP (DHCP reservation) for the TV's MAC address.
IF THAT DIDN'T WORK The nuclear option is to reset the Smart Hub. Go to Settings > Support > Device Care > Self Diagnosis > Reset Smart Hub. This clears all app data and network settings without a full factory reset. You'll have to log back into everything.
HEADS UP If you have a dual-band router, force the TV onto the 5GHz network if possible—it's usually less congested. If the problem persists, a cheap Ethernet-to-USB adapter plugged into the One Connect box for a wired connection is the most reliable fix.