Kohler 3397 flapper

I have a problem with the flapper on my Kohler 3397 staying down. I have replaced the flapper three times in the last 2 years. (So, it isn't the age of the flapper itself)

It seems to work for awhile. But, then it just stops on it's own with no explanation. I have replaced with the correct flapper, and now have tried two generic versions as well.

Any ideas of why this is happening? and any solutions?
Thanks!

Do you use anything inside the tank like one of the cleaning tablets, or any other chemicals? If so, stop!

flapper

I never use the Kohler OEM flapper, always the Lavelle Korky version and never have those problems.

Yes, I have tried the Korky flapper. I have also taken the styrofoam piece out of the flapper thinking that was part of the problem.

It's almost as if there is not proper suction to hold it in place. But I can't determine why that would be. There is nothing that I can find in the path from the tank to the bowl.

flapper

Without the styrofoam it will not stay open the proper amount of time. Suction does not keep it closed. The weight of the water on the top of it, pushes it closed. If it leaks there is some other problem, possibly a cracked flush valve, or a defect in the seal area.