I think the problem is the HUGE black area on TOP of the keyboard? Not the split-mode. If you switch keyboards, does it do this as well? If other keyboards work, this is definitely a Samsung Keyboard bug. If while entering text you rotate the phone, does it 'adjust' to cover the app as well? Have you tried re-sizing the keyboard to see if that might trigger the visual bug to reset?
Yes, it's the huge black area on top covering everything.
Yep, just a Samsung thing, no other keyboards do this.
Rotating the screen doesn't help.
Resizing doesn't help either.
I'd been using MS SwiftKey, then changed back to the Samsung and rebooted, (I have my phone set to reboot twice per week, but I've had the MS keyboard set as default due to this issue). Once I rebooted with the Samsung keyboard, it works now.