Hey
ok so in that case i think you have to wait a bit and work on offpage strongly. Second, check if previous links are on their place, i mean all links! apart from that, in this specific case i think and guess(i can be wrong) google is not considering the site authority like before. you have to work on branding, social signals, social accounts, get some influencers sharing your site something like that. Hopefully you will get all your hard earned ranking back soon! Good Luck!