Lost PNG file metadata: keywords etc.

[galynap43472327]

I have a bunch of PNG files that have lost their metadata: keywords, headline, document title, and description.
All images were keyworded in Bridge on two days (6 October and 22 September). In the files info, there is one date for making and changing images (6 October). It is a date of keywording of most of them. But all of them I made earlier, and some were also keyworded earlier (22 September). I can check it by the upload date on AdobeStock, and sure I'm not crazy because I see keywords on AdobeStock. 
Other images from other dates have their keywords intact. And images from 22 September just located in another folder also have not disappeared. 

I don't believe restore of losted is possible.
But how to avoid this situation? How to backup, maybe, or what? I use Time Machine and iCloud syncing. It did not help in this case.
Is there any shortcut I may accidentally press to delete all keywords from a bunch of files?

[gary_sc]

When you assign keywords and things like that to a file in Bridge, that information is installed IN the file's metadata. Then it becomes part of the file. It can be removed by an intended action, but it cannot be inadvertently lost. 

I'm not saying that you didn't put the data there and now can't find that data, but without more information (such as exactly what your process was to place the data in the image), it's very hard to help. 

Backups are essential to any computer work. But if you cannot find your work in your backups, is it possible you may not have been entering the data properly? When given the option to save, did you save?

Can you supply any more details?

[galynap43472327]

Thank you for the reply.
It is not possible that data was not entered properly. Just because these files were uploaded to Adobe Stock and now are there with their metadata which I entered in Adobe Bridge. I have been doing keywording with Adobe Bridge for years.