Bowl loses water after flush

I have a new Niagara toilet that I installed. When I flush, everything seems fine. There is no leak, no odd noise, or anything else. After the tank stops filling, the water level in the bowl slowly drops. It loses about 50% of its water. This is strange because after the flush the water level initially settles at the right spot. The tank looks to have the correct amount of water in it after the flush, and even after the bowl loses its water. And the toilet that was there previously didn’t do that. And none of the other new toilets do this (we have two other toilets like this in the house). Any ideas as to what could be causing this?