In mid-March I lost more 3/4 of my google keywords according to SEM rush. I noticed my google referrals were down 50%. I still have some good ranking pages, but 3/4 of my words are totally non-existent and it hasn't come back. We don't play any games or use seo black-hat tricks. We have tons of content and a great gob of backlinks. Any reason why that happen? and What to do to get them back up.
Have you checked if you have lost any links that had anchor text for those keywords? I mean, you are asking us to guess why without giving any real information...is there at least a winning price for the one that will guess? just teasing..did you do anything before the loss of the rankings?
Is it normal? You tell us? How long did you rank for that keyword? Google is constantly changing stuff and websites go up and down. Your site must have been trapped in Google filter. If your site is more than two years old or have done over optimization. Your site is likely to be filtered out from some keywords for a period of time. You have to build up links consistency and try to keep your link profile balanced. If your site has too little link popularity and competitors come over your site. Your site has a little old aged. "Sandbox" effect might in place for now. Check if your site has average amount of links but most of them are little to non-quality links. Check if your site has been penalized for selling links or due to malware infection. Have you done any cross linking among websites owned by you and the plan has been found out by Google. Your site has a lot of 404 Error pages (Not Found). Your hosting may not reliable and your site had a long downtime before.
You should also check in google's webmaster tools. They will tell you if there is some problem in your site structure that prevents the spider from indexing you properly.
Its just competition no problem build links. Use your own software to identify keywords etc. (analytics,webmasters tools or custom script).
If you do not do anything, then must be Google did something. If Google did something and not good for you, it means what you did is Google not like. If Google does not like what you did, you maybe need think about and do something else.