Magento 2 - Invalid template error after adding custom shipping method and running setup:upgrade

Question

I have added a custom shipping method module to the app/code folder and after running setup:upgrade I am getting the following error message on the home page:

Error filtering template: Invalid template file: 'product/widget/content/grid_v16.phtml' in module: 'WeltPixel_OwlCarouselSlider' block's name: 'slider\products_0'

I have also run the cache:flush and cache:clean commands.

Edit: Just to clarify, the Carousel Slider widget that is giving the error has nothing to do with my module that was uploaded. The rest of the site is functioning normally.

Any ideas?

Magento version is 2.2.4