Is that limit in hardware or software?
I try 64GB sd-card in RN2-prime on latest 6.1.7 ROM and it isn't work. 32GB works normal.
Then I put it in to my old (3 years) Xperia T on CM12.1 version and it works.
Any suggestions ?
I have a Samsung Evo 128GB microSD card in my Redmi Note 2 and it works great. I used Ridgecrop's fat32format GUI version (http://www.ridgecrop.demon.co.uk/index.htm?guiformat.htm) with default FAT32 allocation unit size to format it. The phone reports 119GB available out of 129GB.
I tried two other formatting methods (Windows 10 exFAT, built-in Redmi Note 2 formatter) but neither worked for me.
I also have a friend with a working 64GB microSD (not sure which brand/model of card) in his RN2. He says he formatted it just with Windows built-in formatter. I understand it only works if formatted on a PC and not a Mac.
I reformated 64GB sd card from exFAT to FAT32 and now it works normaly.
If you are on windows 10 you will need format software
I found it on http://www.ridgecrop.demon.co.uk/guiformat.exe
Run guiformat.exe as admin. and choose size and place of unit(SD card) and run Start.