[Green Baron]

On second thought, it might be pleco damage.

It is the Pleco ! I had the same problem and it took me a long time to figure out it is the Pleco which has been eating the Amazon Swordplant. I had both pleco and Swordplant in 2 different tanks but only one pleco eat Amazon Swordplant ! Once I took out the pleco, the problems was solved and the plant started growing again.