TWRP: Wiped phone, can't put any data onto it through MTP
I had the same issue with MTP not working from TWRP (Windows 10 x64). I used adb push as a workaround way to put update on the phone after disabling MTP from TWRP "Mount" menu:

adb.exe push update.zip /sdcard
adb push open_gapps-arm64-7.1-nano-20170625.zip /sdcard