Hi, Irina, when I opened your file on Ai, the strokes were appearing just fine, they were really small (0,25 pt). One tip that might help you would be selecting the stroke, go to the Select menu > Same > Stroke (you can choose Stroke Weight or Stroke Color..) and then set a standard size for it.
Another tip is that if you are having some incosistencies with the exports, make a duplicate of the file (this way you'll always have a live version with the strokes), and then set the standard stroke weigth, then expand those strokes, this will help you to keep it consistent, but keep in mind that they wont be strokes anymore, they will be regular shapes.
This is just an extra tip, but when I opened your file, the typeface was not embbeded so just make sure if you're sending this to print you outline the text 😉
Hope it helps you!