Swiper slider not working unless page is resized

Swiper’s sliders, in order to work properly, requires you to either:

• Initialize them when they are visible
• Update them when they get visible
• Enable observer parameters
  • observer: true
  • observeParents: true

As stated by @Isaiahiroko and Swiper’s creator (on this issue), executing one of the mentioned topics will solve your issue, for sure!