Description of problem: With gnome-settings-daemon-3.28.1-3.el7_6 (the 7.6.z fix for OSK on GTK apps), I am experiencing the same issue but only over VNC.
Steps to Reproduce:
1. Set up 7.6.z machine
2. Install gnome-settings-daemon-3.28.1-3.el7_6
3. Install tigervnc-server
4. Start vncserver, connect from other machine.
5. Turn on OSK via a11y
6. Try using the OSK on GTK apps like gedit, terminal etc.
Actual results: OSK doesn't pop up on GTK apps.
Expected results: OSK works on all apps over VNC.