Check under Settings > General > Keyboard > Text Replacement and make sure there is not an entry for “Ken”
Failing that, it is probably auto-correct. For some reason the dictionary has decided that Ken is a misspelling of Len. You can try Reset Keyboard Dictionary under Settings > General > Reset.
If that does not work you can turn off Auto-Correct under Settings > General > Keyboard, and live with not having any corrections made (other than Text Replacement). As long as Check Spelling is on, you’ll still get an indication (red underline) of when iOS thinks words are misspelled. Though that’s not completely error free either, you can ignore those mistakes and just keep typing away.
I leave Auto-Correct off myself. I prefer to own my mistakes rather than be embarrassed by proxie.