I have a dual sink drainage issue. I am in near completion of our bathroom renovation. It originally had a dual sink vanity. Each sink had it’s own p-trap leading to the same drain. The configuration is exactly the same. I am not sure how it was before, but now, when the sink to the left drains, water comes up the drain on the right side. Same goes when draining on the right side, the water comes up the sink on the left.
“Each sink had it’s own p-trap leading to the same drain.” is a typo meant to type:

Each sink HAS it’s own p-trap leading to the same drain.