Why don't my apps and transfers stay on my SD Card?!

[makahnation]

I have a cheap ass Samsung Galaxy Luna through straight talk running 6.0.1. Marshmallow and am having trouble keeping stuff locked to my SD card...until I get a newer, more expensive phone, I'm stuck with this starter android and it has shit for internal memory. So obviously it makes sense to clear up internal memory space by transferring files and changing app storage to the SD card. I dont even have many apps and this phone is terrible with usable space. So I use the app ES File Explorer to transfer files to my SD and use the system settings via storage setting to change where my apps are stored, from internal memory to SD. But every time my phone is restarted or shut off, I have to re save all my apps to the SD and sometimes my files...and this is time consuming. My question is why is my phone doing this and is there anyway to move this stuff and have it permanently stay saved on my SD until manually moved, if I ever needed to? Is it the phone itself, being so cheap, the SD card malfunctioning, the operation system, or something else??? Thanks for taking time to help!

 

[Hadron]

I've heard of apps moving back to internal when updated (do you allow automatic updates? If so this might be moving apps without you knowing), but not on a reboot.

As for files, what sort of file? Are you sure they are being moved back rather than recreated (app that owns the file sees it is missing - because it has no way of knowing that another app has moved it or where it's been moved to - and so recreates the file)? It will depend on what the files are, e.g. music should not move back, but a data file belonging to a particular app should only be moved using that app's settings (if it has such a setting) because otherwise it will not be able to find the file after you move it.