This just happened to me after restarting my vita. I had removed the SD card, put it back in and restarted. None of my apps showed up except for Vitashell and Molecular shell and system apps. I turned off Vita, took out SD card, reinserted...
I may try the new ram site, and download more RAM to my Switch. Not sure if ddr3 is the right ram
for it tho. Edit- no it uses floppy Ram, just like @AncientBoi