User updated the image on mysite. For a some user thumbnails versions _LThumb.jpg, _MThumb.jpg, _SThumb.jpg are not created under User Profile/Profile Pictures library on mysite.
You need to run the following command to update the profile photo store and thumbnail versions.
Powershell command :-
Update-SPProfilePhotoStore -MySiteHostLocation https://mysites -createThumbnailsForImportedPhotos.
There is a possibility of this not working for all the users in the first iteration . Run it again and you will see that your problem is solved.
Don't forget to run Crawl after this if you want to see the updated photos reflected in your sites.