Hi,
this bug has been well documented I believe (the placing large stone wall when in water bug). Placing a large stone wall when in water causes my client to crash, so that I am unable to tab-out and a system restart is required. On one occasion the crash caused my steam installation to not recognise that Atlas was installed, requiring a recheck and repair of all game files.
As the bug is well known, I will not go into too much detail on how to recreate it, but I did want you to know that I was able to circumvent the bug occurring by hanging from another large stone wall with a grappling hook and snapping the new wall in place. This works 100% of the time, no failures. I thought that knowing this, it may point you in the right direction when ironing out this bug.
I play on the astral-atlas unofficial server cluster.
Cheers,
Waylan.