Page Ranking in Google SERP

Define "I was doing SEO for a website" 

Because if that was the only change then it could be you have done something wrong. So what were you doing? 

did you build any backlinks regardless of if you think they are spammy

Could have been hit by Google's MAY 2020 update. Although "ranking for 7 days" looks like personalised results to me, to be honest.

Firstly check it's in the index, so type into google:

"yoururl.com/gff/fgfg"

If it's not there, yet your manual penalty section in Google webmaster tools. 

If there are no penalties, then look into increasing the quality of your page(s), & if you genuinely think your website is flawless, then seek professional help.

You better check your website. If there is any mistake you will notice. And if not, then take a look at some of them.