[lancemcv]

I have been using a Pro Tools native system to record live shows over the past 5 years with the same 2012 i7 quad core MacBook pro with Pro Tools 10 then 11 then 12. I have never had a failed recording (fingers still crossed) plus some shows I switch cameras via blackmagic switcher app while pro tools is recording in the background and record video at 1080p 20mbps to the same SSD drive installed in the DVD slot which is why I love the 2012 MBP, it has ports and you can install a SSD in the DVD slot. I don't like recording on the system drive even if its an SSD.
It comes down to not using an OS that is not supported and the fact that you are using a firewire connection with an unsupported driver to add to the problem. You most likely just got a cpu spike or who knows what error. Its one thing to experiment with an OS on your own time but too risky to do it on someones else dime. Its not pro tools or your laptops fault.
I would setup a new boot drive, with High Sierra. and as others have said you should always have a backup recorder, which can be tough when recording off the FOH board and if your mixing monitors from FOH. The way you are doing it off the Avid board there is no simple way for redundancy. You would need to record off a monitor console or bring in a splitter and have a second record system which is usually the main record rig and the better way to record shows with its one set of mic pres. Sometimes I have the FOH engineer do the backup record but I usually try and have my own backup and still have the FOH record as well, like a Madi recorder, JoeCo box, Dante is good as you can have several laptops recording off the same main system, but backups cost money if the band doesn't have the budget then its their risk but its on you to have the main record rig that you know is solid and not mess with unsupported software for a job. It may work one day and not the next.