Take yourself out of the picture so to speak. Give your customers a handful of blank shirts same brand and color and ask that tey wear them for a month then review.
This removes all of your printing process other than ordering and unboxing
I have no idea what is going on here except when I was a young ladd I worked on a bunch of cars.
My shirts always ended up just like you see in your photos. the bad actor was the dried up caked on battery gunk on the terminals of the then refillable batteries. All was fine as I leaned over the dried up gunk and brushed it off my shirt. When the shirt hit the wash everything changed.....and there they were acid burn holes, exactly like you have there, isolated , localized and no evidence of stains or other stuff...just holes.
I would look at the operation to see if they are using things like cleaning / disinfecting products.
Here is a quick Google search for restaurant cleaning chemicals , I'll bet there are some fabric foes in some of this stuff.
https://www.google.com/?gws_rd=ssl#q=restaurant+kitchen+cleaning+chemicalsThink of this the dehaze products we use on screens contains caustic soda it will damage fabric. It is also used in some food prep services as a cleaner .
No doubt in my mind this is sourced at the customer simply based on what I see and remember from my own experience and more so the isolated areas of the damage. Ask the customer does this happen on the back of the shirts?
Most likely not because that side of the shirt is away from whatever process that is the cause of this failure.
mooseman