I recently upgraded to LR6. I have hundreds of keywords but now, they do not all display; only 'a' thru around 'n'.. They are all still there - I can still access the missing keywords via the '/' command, but I can no longer browse keywords starting with the letter 'P' and forward. What has happened to my keywords?
If you are on Windows and have more than about 1500 keywords at any one level, LR chokes. To work around this bug, introduce hierarchy to your keywords; see this Adobe help article: Keywords missing.
This is a long-standing bug that Adobe has inexplicably failed to fix for many years. Please add your vote and option to this bug report in the official Adobe feedback forum: Lightroom: I cannot access the whole keyword list to edit. This will make it a little more likely that Adobe will prioritize a fix.