Is there a non-root solution for the MM Portable storage issue (at least on Boost) where it will only let you "Move to SD" to around 500MB and then it says "Not enough storage space" when in reality there is 25GB available on SD card?
Short answer: free up SD space. Your manufacturer has probably set a limit in the OS which tells it not to move apps anymore after the card is full to a certain arbitrary amount which is unrelated to its actual formatted capacity.
Long answer:
I have recently purchased the Alcatel Pixi 4 and put a 128GB SD on it. I was happy to find that the card worked just fine despite the device being advertised as supporting only up to 32GB cards.
After formating the 128GB SD as internal memory and moving my songs onto it, I found I could no longer move apps. I was using up 35GB, but still had plenty of room. Android, on the other hand, would keep telling me there was not enough space.
So I figured: what if there is a software limitation that will make Android think there's not enough space because the phone simply wasn't meant for more than its advertised capacity?
So, what I did was to go ahead and delete my songs leaving just some 4GB used up. Voila! I could successfully move my apps again.
Apparently, the manufacturer is able to set a limit on how much data you can move to the SD. Or, rather, how much space on the card can be filled up until the system will no longer allow you to move more apps. And that limit is arbitrary having nothing to do with the formatted capacity of your card. All you have to do is to keep yourself restrained to that limit. For my Alcatel Pixi 4, that seems to be 32GB.