Have you tried this ?
viewtopic.php?f=16&t=814
Always explain more the situation, "problem with HD" - that doesn't explain enough for someone to help you.
It is weird situation if you are having problems both on wifi and wired connections. I had issues with a bad router that gave wifi issues. Upgraded my router to a ASUS router and even the wired connections are more stable.
Comparing your SmartTV to TVbox connection can be mistake if perhaps the tv is connected on 5g wifi and your TVbox is limited to the 2.4g wifi network. In your router settings it should show what devices are connected and over what network band: LAN, wifi 2.4, wifi 5.8.My smart tv (panasonic viera) plays smoothly over wireless network.
So even physical media has HD issues. Could me something simple as HDMI cable is old and faulty or not connected properly. Or may be a settings issue, something got changed and is causing the problem. Example the Auto-Framerate is a big issue with Amlogic and AtvX has option for Off, Level 1, Level 2 and I always recommend leave that setting off. You mentioned Kodi, some people report problems with Kodi 18.2 and went back to 18.1. So in that case it is an app software issue.