The snackbar's action seems to disappear when a message is long.
how long? if it is too long you may consider using other component instead of snackbar. MD specs said
Very short text strings
Snackbars should contain a single line of text directly related to the operation performed. They may contain a text action. They cannot contain icons.
@zachguo is correct, but it's still undesirable for the button to disappear when the text is longer than the available space, particularly on mobile, since multi-line layouts aren't currently supported.
The text truncates at a word boundary, but only when it overflows the div that contains it and the FlatButton, rather than leaving room for the button.
@oliviertassinari - multiline layout for mobile would be a feature request, but I think the way the button pops below the Snackbar when the text is longer than the available space should be considered a bug.
If you are using it in normal web-app(not mobile-app), this should work:
<Snackbar
style={{ pointerEvents: 'none', whiteSpace: 'nowrap' }}
bodyStyle={{ pointerEvents: 'initial', maxWidth: 'none' }}
/>
Most helpful comment
If you are using it in normal web-app(not mobile-app), this should work: