Modular Industrial Catwalks Set navigation problem mentioned in a review

Hello everyone.
I have recieved a review on my product:

and question:

I have a problem to understand what user means under navigation. Tested stairs meshes for ability to go up and down using standart epic skeleton and it works fine. Here is a video of it:

My product is:…da1d099fe81168
Also i have a request for people who bought my product: please let me know if you have same issue or any other problems with this set.