You’re not showing us the code that comes before this statement, but undoubtably there is a select statement that has produced no matches. When that happens, any following formulafill statements will be skipped. If you want to fill all records, be sure to put a selectall statement above the formulafill statement.
When you put in the debug statement, that cancels the after effects of the previous select statement. This is really a bug in the debug statement, it should remember that there had been a failed selection and keep that status when you resume, but it does not.