This is quite repeatable here with the current version.
I made a new document and added a basic contact form widget. The I selected one text input field and changed the font to a web font and changed the text style to roman rather than italic. Now when previewing in browser there is an error for each frame in the form, e.g.:
“Text frame on page 'Home' (with text 'Enter name') uses an unsupported variation 'Italic' of web font named 'Nunito Regular'. 'Italic' will be simulated.”
The next time the document is previewed in browser there will be no error, but make a trivial change such as moving the form slightly, and the same error will return next time the document is previewed.