Facebook ads. When I duplicate ad and change objective. Ad resets

How can I keep the same stats?

I was able to do this before but now it resets. Is this new fb thing?

It's always been like that, ads optimize on the adset level. Every new adset goes through a process called the "learning phase" Look up the facebook article:
"About the delivery system: Learning phase"

PS. Read all the facebook business articles you can - there's lots of opinions out there and these are the articles that always come closest to the truth for obvious reasons.