Tools to test mobile compatibility

I'm working on a web application which has few forms. Form has multiple dropdown lists and I'm using Select2 for it.

When I test it on chrome (mobile simulation), it runs fine but when I test in on mobile(OnePlus Two, Nexus 5), one dropdown works intermittently. Sometimes works fine, sometime toggles and other times does not opens at all.

My initial guess was it takes time to load since this dropdown has over 1000+ options. There can be other issue, might be in my code as well.

But just want to know:

1. What are different options that we can use to test a web application for mobiles?
2. Are there any such issue that runs fine on simulator but fails oon actual device?
3. Also when we simulate on browser, keyboard does not appear. Can the aspect ratio of control and keyboard cause any issue?

Known sources for simulatiom

1. Chrome Dev Tools.
2. Browser Stack.

Thanks in advance.