In kate when automatic spellcheck is turned on, it does highlight mis-spelled words in the beginning, but after a highlighted wrong word is corrected, the highlighting does not persist for other mis-spelled words.
Of course toggling Ctrl-Shift-O works but it is cumbersome.
This was not how automatic spellcheck used to work in kate.
I created a new user, with new KDE and other settings from the defaults, and typed some words in kate. Wrong ones were highlighted. These were corrected. Then I typed some more, this time with some words correct and others erroneous. The erroneous ones were not highlighted.
Ergo, automatic spellcheck does not seem to persist throughout an editing session. It starts off showing errors. When those errors are corrected, and I resume editing, new errors are not highlighted. If I use Ctrl-Shift-O and toggle, things work again. But not until then.
So, both a new user with fresh defaults, and I , experience the same non-persistence of automatic spellcheck.