Created attachment 106313 [details] PNG screenshot of q́ in Kate. When entering a character followed by a unicode combining diacritical mark, if the letter/diacritic combination does not appear in unicode as a single character, the diacritic will be drawn one character to the right of where it should be. KDE 5.28.0, Qt 5.7.1, xcb
Created attachment 129542 [details] Kate showing combining chars in Noto
Seems to be a font issue. Fixed width fonts don't do that as it can affect selection and other stuff. Even here in Bugzilla it shows as your screenshot. Attached an example in Noto. To be closed.
This was either a font or Qt issue. Please add a comment if it still happens with recent versions (Qt 5.12 or newer).