Some Images Disappeared from Media Library?

I suspect that the missing file, which is somewhere in the wp-content/uploads folder, was not moved to the new hosting place.

You could use an FTP client to move all images from the old hosting place to your local computer, then use FTP client to copy only the newer images from your local computer to the new hosting place (selecting newer only would be a bit faster than copying everything).

It is also possible that the database entry for that image didn’t get updated to the correct URL on the new place. This would be especially if you changed domain names when moving to the new place.

If you have the original copy of the 2015/10/R_151023.jpg file, you could upload it manually to the 2015/10 folder.