I am not a plant expert. I am just going to share some thoughts and ideas based on several books I have. One book is, "The Natural Aquarium," by Satoshi Yoshno and Doshin Kabayashi 1995.
My experience, (and what the books say), is that Amazon Swords need high lighting requirements. A tank your size should have 60 watt incandescent, which is 800 Lumens, or around 20 CFL. They are saying to keep the lights on 15 hours a day, unless it is next to a window, and in that case 12 hours a day.
They use river sand, (again I am just using gravel myself). At least a sand/gravel combination seems to be what the books say is best.
They are using a canister filter for two of their tanks, but for the all swordplant tank they are using an outside filter with three chambers.
They have about 20 fish showing in their pictures.
They do a water change 1/3 every 2 weeks.
They use fertilizer. Perhaps, your Catfish population is a bit too high? Those fish could be eating nutrients that the plants need?
Here is a big difference that I think you have hit the nail on the head as to the problem. I think that it is possible that your filter situation you are talking about is somehow breaking up the CO2 on one side of the tank. Amazon Swordplants love CO2! The only time I have had success is adding CO2. The book says to add CO2, and the Japanese independent fish store also had great success adding liquid CO2. In the old days they added CO2 by overpopulating the tank with fish.
If you are not doing it, and you can on a 29 gallon, you should make a CO2 Generator. How to Make a CO2 Reactor for an Aquarium: 11 Steps - wikiHow
This is easy to do with a 2 Liter bottle!
It will last for around 2 weeks and then will need to be changed again. 1 to 2 cups of Sugar, 1/2 TSP Yeast, water and you ready to go. Cheap, and it works!