Yes, there are 2 possibilities.
1) It doesn't like what you are offering it to eat.
Check freshness of your food and if not the issue, check with where you got the fish to see what they were feeding and duplicate that.
2) The fish has an internal condition making it tough for the fish to swallow.
This will require use of an antibiotic to help reduce the condition.
My gut tells me that it's #1 over #2. The fact that it rejected some of your offerings totally while testing others says to me that it doesn't like the food.
Hope this helps