Protein Bars

You could use Inulin for the binding of bar to maintain sugar free.

Gum Arabic is also a good food glue, for cereal bars or protein bars. As a soluble Fibre it good prevent some drying out.

Is there any fat in the formulation?

Good point, fat is important for smooth texture. Also water content of product is important.

And to keep it a little soft you can try glycerol maybe.

Also look at this topic.

https://feople.io/t/need-help-with-protein-bar-recipe-for-business/1001

Sounds like your water activity is not stable

You need to know the precise sorption properties of your samples which will tell you expected performance in different humidity environments etc

https://www.metergroup.com/food/articles/lowering-water-activity-humectants-step-step-guide/

yes, coconut oil.

Could it be that the chocolate coating affects the texture of the product?

What is the ratio of glycerol recommended to add?

Thank you!

Thanks!
What is the ratio of Gum Arabic is recommended to add?

You could also try Oats Fibre, excellent water binder, but water still there for softness. Try 1%, other soluble like gum Arabic, Fibre gum from Nexira also good, 0.5-1%

Water trying to penetrate against unprotected Chocolate coating can also have preservative problems, potassium sorbate may be needed. A PGPR addition to chocolate coating could help with barrier protection of chocolate compound coating.

Thank you!
I will try it!