In a non-responsive project text containers are converted to bitmap images, which can be the reason for the appearnce of blurriness if you upscale.
To avoid that you need to make sure that text is rendered as text on runtime. That can be done by making sure all text is dynamic. That is the case when text has an inserted variable. You can use an empty variable for that reason, add it at the end of the text, and it will be rendered on runtime. Beware: you need in that case to use either a websafe or a Typekit font.
How can I generate the empty variable?