Soap bar won't remove any chemicals. It will only take care of things like oils and butters. It's unlikely that an oil from the soap bar would remain on your hair--think washing your hands or body. Soap doesn't stay after you rinse off. Wash your hands with the soap, if they don't feel coated--your hair shouldn't be coated, either. pH of this bar is 8. I have moderately hard water (3 of 4) when setting up the espresso machine. Both DH and I use these bars as our shower soaps--don't have unusual issues with soap scum.

It takes hair a few washes to acclimate to using soap bars on hair. When you first use it, your hair might feel waxy or "odd." As soon as you apply rinse out, that should go away.

One might need a stronger surfactant to remove oil if they "goobed" it or butter on their hair (for a DT or prepoo.) The insignificant amount of oil or butter from what a typical user would put in their hair when styling wouldn't require all that much attention. Most of it is absorbed into the hair.

I have fine/low porosity hair and use really rich products. Never have an issue with oil/butter build up over the past five years. When I go to the salon for my haircut/highlight, I do bring a product like CJ Daily Fix with me. The shampoo guy refuses to use a rinse out conditioner because my hair is so healthy (he just doesn't get it.) The only time I use a lowpoo is if my hair is "odd" from an ingredient it doesn't like. That could be every few months.

I do have issues with polyquats. There was a thread a while back where someone mentioned that they stay away from all ingredients that end in "ium," because of build up. This included Behentrimonium Methosulfate--which is in a lot of products. In follow up reading, it was mentioned that some other "thickeners," like guar gum, can also cause that kind of build up.

Bottom line is that it could be any chemical in any product that's built up and caused that gummy feeling. If you have CJ Daily Fix, try that first. Coco b is a gentle surfactant. It also has a chelating agent to take care of the minerals. If that doesn't do it. Move up to something a little stronger.
3a (Corkicelli), highlighted, fine, low porosity

HGs: Anything Sevi; Curly Kinks Satin Roots, Curlycue ReNew and Coil Jam; homemade FSG and okra gel; soap bars; UFD Curly Magic; Botanical Spirits Jellies, CJ Repair Me, Aloe Fix