Wrench no longer working due to old theme

Yes it’s probably our theme. It’s quite old. However no one had touched any code locally in five years and yet there have been a number of problems arising.

I’m not interested in placing blame though. I am interested in solving the problem.

How does one test for problems?

Are there acceptable methods to create a working navbar for a custom theme? (Ours is an ancient version of bootstrap/jquery)