Sometimes, when you are downloading multiple files, they get download into different folders automatically, depending upon the size of the files.
All the APK's will be inside the "Downloads" folder, but sometimes music/video files get save into "Music/Downloads" folders.
And if multiple files are download, for example- One APK and Two Music files. Then, they will be save inside the "Downloads" folder, but music files will be inside the "Music" folder, and APK files will be in the "Downloads" folder
So you have to find the actual download folder and find files.
How to do this: Open the ES Explorer app and tap on the "Up" button.
Now, you will be able to see the list of folders/files which you downloaded recently. Find your file by scrolling that list.