A recent Lightroom update broke the way Lightroom was auto-suggesting and autocompleting keywords for me. About two-thirds of the time, when I created a new keyword and then went to use it on a different photo, it wouldn't appear in the suggestion list. Old keywords worked fine, and the tag was absolutely there. If I opened up the full keyword database it would be present, in the right spot, and the correct photos would be linked to it. But it just wasn't an option in the autocomplete dropdown.
The issue was not universal, either; some days it wouldn't happen at all and every new keyword would be immediately indexed correctly, appearing the moment I started typing them in. But once a keyword had fallen into whatever disassociative pit was causing this forgetfulness, it never came back. No matter how many times I restarted Lightroom, deleted the keyword, changed it, or used it, that entry was invisible to the search functionality.
The result was irritating, to say the least. Duplicates and misspellings began to appear. I'd have to look up terms multiple times or need to copy and paste between photographs. I have a fairly specific keyword hierarchy that occasionally includes things like full binomial names, so a lack of search and autocomplete made tagging incredibly inefficient, particularly as the number of "missing" keywords began to grow larger and larger.
I've tried hunting down potential fixes in the past, but it seemed like only my install was having this issue. No amount of DuckDuckGoing seemed to yield results, nor did searching through Reddit archives. I did try the official support forums, but the search there is notoriously bad so I didn't try too hard. At least, not before tonight.
Getting fed up for the umpteenth time, I spent another hour or so scouring the web for potential help, finally stumbling upon an Adobe support thread. This crosslinked to another thread, which crosslinked to a third thread, and in there I finally found an answer. Irritatingly, not from an Adobe rep, who instead had just abandoned the thread as "too old" after a couple of months when users kept adding to it. Instead, my saviour was another annoyed customer who had seemingly just begun deleting stuff to see if it helped. Luckily, it had.
So for anyone else out there experiencing missing keywords (or, based on the other comments, suggestion lists that contain duplicated keywords or keywords that have been deleted or renamed), here's the trick:
Delete your Helper.lrdata file.
You'll find it alongside your "catalog" file, normally in your root Lightroom folder. For some catalogues it appears to be a folder with a "helper.db" file inside, in which case delete both the folder and the contents. For me, it was just an LRDATA file stored at the same level as my catalogue.
As ever, make sure Lightroom is closed first and make a backup copy of the file somewhere else before deleting it. You shouldn't need to do either, from what I understand, but it doesn't hurt and it will stop edge-case bugs. When you relaunch Lightroom, the program will generate a new file (or folder) to take its place and, hopefully, your keywords will be back to working as they should. It worked flawlessly for me.
If you're still having issues, it doesn't hurt repeating the above step once or twice, but you'll also find the support threads I found most useful linked below. They may have some new information by the time you need it 🤞 One small tip I saw in a few places was to go into Edit → Catalog Settings → Metadata and hit the Clear All Suggestion Lists button. Can't vouch for that myself, but it's repeated enough to likely be useful for some people. Good luck!