Certain letter together character to different character or disappear

i am new to font creator and i am having an issues when i type fi together it changes to a different character and i don’t know what. Then when I type fl together is disappears altogether. Please Help
fi.JPG
fl.JPG

Open the OpenType Designer (Ctrl+F8) and look at the Standard Ligatures. fi ligature should be composed from f+i; and fl ligature should be composed from f+l.
Standard Ligatures.png