I think that after update of KF to version 5.37 in view hex+char appeared some strange highlighting. Also this was happened in char view, but after couple run there is no highlighting. In meantime I only set "profile view". Maybe this is related with incorrectly detected highlighting by KTextEditor component, because similar strange highlighting I observed also in first run of KWrite, when I opened simple text file. Here I set highlighting to "None" and all back to normal. In case of KWrite I'm sure that it happened after update KF to 5.37 version.
Created attachment 107362 [details] highlighted hex+char view
*** This bug has been marked as a duplicate of bug 383848 ***