Hi, After updating to version 7.20.4, backup files from Mikrotik iOS 1.2.18 are no longer visible in File.
Which device in particular? Certain devices (generally those with less than 32MB storage space and more than 64MB RAM) will have /files rooted on RAM disk (and permanent storage is mapped on /flash). Which means that any files on storage root will be removed with each reboot (not only after ROS upgrade).
Note 1: storing backup files on the device itself is not very safe, there are problems which render device unusable and only netinstall can revive such device ... and netinstall includes formatting internal storage.
Note 2: backup files are only truly usable[1] when used on same device and with very same ROS version where they were created. This might not be prominently documented, but was stated multiple times on this forum by MT staffers (@normis). This wisdom might be built into some apps (I'm not entirely sure what does "Mikrotik iOS 1.2.18" mean ... I'm not aware of "Mikrotik iOS" and I don't know any contemporary MT software with version number as low as 1.2.18).
[1] Yes, backup files mostly work on different device of same model as backups were made on ... but after restoring some things have to be "corrected" if original device is still present on same IP subnet.
And yes, backup files work most of times on newer ROS version mostly fine ... and they work also on slightly older ROS versions if there were no major changes in functionality or configuration style.
I think he is referring to Mikrotik iOS app connecting to a Mikrotik device. That one has version 1.2.18.
In that app he can not see backup files anymore in Files.
At least that's how I understood ...
But that needs to be confirmed. Anyhow, I only use Android and there all is ok 
Yes, you heard correctly. After updating to version 7.20.4.
OK, that makes it a bit more clear. I have updated your title to make it equally clear for everyone reading this thread.
What Mikrotik router are we talking about here ?
From my side, no idea since I don't use iOS anywhere.
Maybe other users will come by who also use iOS app.
In parallel you can try to create a ticket to support with the necessary info and screenshots.
You may also try to downgrade again to previous version to see if contents of File come back.
Also use that info in your support ticket.
And then, once that support ticket is created ... move again to 7.20.4.
It's not the first time something doesn't work the first time but after downgrade/upgrade it does work as expected.