Nexus 7 2013 WiFi (flo) bootloader unlock fails

Update: I don't know what I did differently apart from factory resetting it a lot of times, but it finally went through and unlocked. --- I'm trying to unlock the bootloader on my Nexus 7 2013 WiFi 32GB (flo). I turned it off, pressed power button + volume down, which soon greeted me with "the bootloader". I then ran fastboot oem unlock which prompted the tablet to ask me whether I really want to unlock the bootloader, and I subsequently navigated to yes using the volume keys and confirmed with the power button. Following that, this was printed to my computer's terminal: (bootloader) Unlocking bootloader... (bootloader) erasing userdata... (bootloader) erasing userdata done FAILED () Finished. Total time: 17.372s As you can see, it only says FAILED (). No error code. Looking at photos of others unlocking the bootloader, it seems that the next step should be erasing cache, however it evidently does not progress there. I can still boot into Android though. First boot initially greeted me with an "erasing" screen which had an Android on it, and all user data was erased (as expected). I did try repeating the procedure once more after letting it boot Android again but the result was the same. Other things I have tried are manually formating the userdata and cache partitions via the recovery menu and factory-resetting from within Android, however neither of these were fruitful. I have tried 2 different computers and 2 different USB cables but they yielded the same results. How might I go about resolving this so that I can unlock the bootloader?