You're just five weeks post op. You have had a major revision of your upper GI tract, and have likely irritated your vagus nerve, which is going to take some time to calm down. There is swelling at the wrap site, and things are still healing.
If you can just try to give yourself a chance to get some healing behind you before jumping to conclusions, you may find that many of the things that worry you will resolve themselves on their own.
Any type of food can bother you right now. Your stomach is in an uproar--swollen, and if I remember right, struggling with pre-surgery gastritis. This takes a long time to get better.
Your stomach will not be right for many more weeks. Don't assume the worst, or jump around looking for reasons or solutions to your problems. Just make the best of it, relax, surrender to the recovery, and remember that healing from this surgery will take time and can't be hurried.
It's very common to have some food/drink held back at the wrap site--especially at 4-5 weeks. There is peak swelling right now, and it will take several weeks for it to go down.
Many continue to have some food held at the wrap site indefinitely. I know I do. I have to remember to drink water after eating, to be sure and wash the rest of it down. It's really not a big deal. Sometimes it can be irritating, depending on what has been eaten, and if I forget to wash it through before bedtime. Still, I wouldn't trade that problem for the ones I had prior to my surgery.
When I had my barium swallow after a year, the radiologist said that some of the barium was retained in the esophagus and traveled up and down the esophagus, presumably propelled by air escaping from my stomach. Honestly, I couldn't care less. It's something I have to deal with, and I gladly accept this little quirk. Overall I have done just fine post-op.
So...try not to worry. You had lots of issues prior to your surgery. All that acid has left your esophagus burned, no doubt, and it will take a long time to heal. A Nissen doesn't magically undo all the damage that was done pre-surgery in a few weeks. It takes time and patience.
Try not to panic. Things will improve over time.