This is something that has always bugged me, like for ever 
I occasionally type in a value for the kerning. Sometimes this causes to freeze/unable adding kerning by the keyboard. Not always… Only way to reannable this is by clicking on another tab and go back again.
Maybe worth looking at it…
Are you sure the edit view has the focus and not a text field in the info box?
I haven’t found a pattern. Sometimes I type into the info field and then everything works fine.
Sometimes it doesn’t. You can still skip between glyphs (fn+arrows), but adding kerning with key board doesn’t work.
I think I even noticed you can type a letter and then it doesn’t work either…