I've never had or seen this problem in my repair work but have heard of it.
The black box along the filler tube is referred to as a "Tank air filter" by Kia and Hyundai. It's part of the emissions group and "might" be your problem.
This filter is a service replacement item. Consult your owners manual for the interval recommendation.
The bottom line is if this filter has never been replaced, I'd do it. It might fix your filling issue providing the filler pipe has no issues.
Most dealers will avoid or overlook this item.