I've been using FTM for 20 years and would have to agree with the FTM support. I've never experienced FTM "losing" data.
I agree with the previous post that you probably posted the info to a different file - a backup?
Or... A different person - a spouse or child or person with the same name. I've done that on several occasions. Posted an occupation for the father to the mother; or even a parent's data to a child or a child's data to a parent, by accident. Try searching by the filter at the bottom of the index for a text string that you can recall in what you think is lost. You can search in individual facts, or throughout your file (use the "other" selection.). Or use Edit > Find.
What type of info is missing? Text in a fact description or notes, or a whole fact? A whole person is gone? A Spource? A media item - was it attached to a person or fact or source?