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• First you have to unmount the disk

    diskutil mountDisk disk0
  

• Check the partition layout, then remove the two partitions:

    gpt -r -vv show /dev/disk0
  
    gpt remove -i 2 disk0
    gpt remove -i 1 disk0
  

• Since the (Apple-)EFI usually has a fixed size we can easily add it with:

    gpt add -b 40 -i 1 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B disk0
  

• With the start block of the EXFAT partition and Size (the volume size found with Method 1 or 2 above) we can also add it:

    gpt add -b NewStartBlockEXFAT -i 2 -s Size -t EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 disk0
  

• Remount disk0 with:

    diskutil mountDisk disk0
  

• Quit Terminal, Calculator and wxHexEdit and open Disk Utility.

• Check your EXFAT volume for errors.

• First you have to unmount the disk

    diskutil umountDisk disk0
  

• Check the partition layout, then remove the two partitions:

    gpt -r -vv show /dev/disk0
  
    gpt remove -i 2 disk0
    gpt remove -i 1 disk0
  

• Since the (Apple-)EFI usually has a fixed size we can easily add it with:

    gpt add -b 40 -i 1 -s 409600 -t C12A7328-F81F-11D2-BA4B-00A0C93EC93B disk0
  

• With the start block of the EXFAT partition and Size (the volume size found with Method 1 or 2 above) we can also add it:

    gpt add -b NewStartBlockEXFAT -i 2 -s Size -t EBD0A0A2-B9E5-4433-87C0-68B6B72699C7 disk0
  

• Remount disk0 with:

    diskutil mountDisk disk0
  

• Quit Terminal, Calculator and wxHexEdit and open Disk Utility.

• Check your EXFAT volume for errors.

In comparison the result of sudo gpt -r -vv show /dev/disk2 of my 4 TB device created in a VM and formatted with Disk Utility looks like this:

The result of sudo gpt -r -vv show /dev/disk2 of my 4 TB device created in a VM and formatted with Disk Utility in comparison looks like this:

In comparison my 4 TB device created in a VM and formatted with Disk Utility my sudo gpt -r -vv show /dev/disk2 result looks like this:

If you get a significantly smaller start block (=<409640) stop here, because you probably didn't partition your disk with Disk Utility previously.

In comparison the result of sudo gpt -r -vv show /dev/disk2 of my 4 TB device created in a VM and formatted with Disk Utility looks like this:

If you get a significantly smaller starting block (=<409639) stop here, because you probably didn't partition your disk with Disk Utility previously.