I have one keyword which disappeared

[Yellow2000]

My site currently ranks for over 2000 of which 92 are in the number 1 position. Im very active with this site. My Main  keyword is a two word keyword ,I have never been below the position #30. Has always been at best 3rd and fourth page. I rank primarily for mostly 3 part keywords and 4 part keywords. However , I noticed about a month ago,The main keyword no longer showing up on serp tools .Moz included. At first i was getting wierd results using keyword tool .Not moz serp tool. I would get different result every time i checked it. When i tried to verify these results ,Only to   find my site not at the projected page and rank. After more than a month now this particular keyword is no where in site. Im still getting traffic fom all the other keywords but im a bit confused over this. I thought my main keyword was about to be on the bottom of the 2nd page but instead seems to be completely gone.

[ShahzadAhmed]

Hi Robert,

There was a google update in March which Gary Illyes jokingly referred to is as "Fred" - Fred Update. The main purpose of that update to target websites with thin content, low-quality content or spammy links. I think your keyword is the victim of that update. Hope you find your answer.

Thanks,

Shahzad A