Got the exact same thing with my Ipad Mini 4 wifi 16GB, i tried updating/restore on 4 different computers (2 were macbooks)using 3 different official apple USB cables on every single port i could find. Same Error 14 every time. i confirmed i was running the most recent Itunes 12.7.4.80.
I took mine to the apple store yesterday, they tried on 2 different macbooks with several cables and they also got the error 14 everytime.
They basically told me i now have a brick and theres nothing they can do since it is out of warranty. They said it maybe the logicboard is bad but couldnt tell me for certain and wont take it apart to see the problem.
Took it to a local 3rd party technician, confirmed i also had a brick. so now i'm contemplating if its worth trying to get a logicboard or just sell for parts.
sorry man. hope yours can get fixed some how but if its the same issue as mine.... :(