1) Reboot your device into TWRP Recovery.
2) Go to Wipe menu.
3) Go to Advance Wipe.
4) Select Data and go to Repair or Change File System.
5) Click Repair File System. (If not fix, go to step number 6)
6) Go to Change File System.
7) Select Ext2 and swipe to confirm.
8) Now change back to Ext4 and swipe to confirm.
9) Now go back and check if your partions can be mount or not from Mount menu.
10) If not fix, repair your Internal partition. (This may wipe your Internal storage).
OR Unlock your bootloader again.