Font glyphs not working properly after export

So I am new to Glyphs and still currently using the trial (I plan on purchasing Glyphs once the trial expires).

I have created a very basic hand-written font with some additional glyphs, however, once I export the font and try to use these, they only work if I try to use them in the middle of an existing word which uses my font. If I try to use these glyphs at the end of a sentence using my font, they will show up as Myriad Pro. I have posted a screenshot below to better visualise what I am trying to explain here.

So as you can see, in the top line of text, I was able to use the glyphs if I put them in the middle of a word, but on the bottom line of text, they just show up as Myriad Pro.

In what app are you testing?

Did you read this:

Most likely you are typing a letter not covered in your font, and the app defaults to a fallback font.