Website only sometimes showing in google under a keyword
For the past few years when I typed in a specific keyword into google, my website ranks at around number 6. For some reason in the past 2 months the website disappears under that specific keyword and doesn't rank at all. It disappears for a few hours but sometimes it can be over a day but then appears again. Ive seen this happen for a few minutes but now on a daily basis it's showing and then not showing. Last week it didn't show for around 3 days under that specific keyword.