@Thomas Toffalori - Unlike the newer 2018 model which have a T2 chip, yours doesn’t offer this so you do have a means to easily boot up under an external drive.
I would see if the problem is still present when you are running off of the external. Create a bootable external drive with the same OS version you are currently using.
Using the Option key when you start your system you’ll gain access to the Boot Manager to select the external drive.
Let us know if that made a difference!
Reference: [https://support.apple.com/en-us/HT201255|Mac startup key combinations]