The Kunena team has announce the arrival of Kunena 6.2.6 [K 6.2.6] which is now available for download as a native Joomla extension for J! 4.4.x/5.0.x. This version addresses most of the issues that were discovered in K 6.1 / K 6.2 and issues discovered during the last development stages of K 6.2
Question
Cursor Keys (left & Right) not working in Editor
SimREVS wrote: Has anyone an idea what maybe causing this?
I cannot be sure but the most likely explanation is that you have a piece of Javascript running on your pages that are interpreting the cursor key events in a way that is incompatible with Kunena.