I agree with peacemaker's points.
'Glass thickness, age of use, and method of transport are some factors that may contribute to the conditions'
A bit of what i've read before::
uneven base (or at an angle) with bigger tanks causes uneven pressure on the glass.
uneven surface, twists the glass, weakening it.
Like the expert says, the stand could be the cause too.
The floor/ location must b ensured that it can take the wieght and is not too slanted too.
Whether the stand is no good?,, the experts must come in n see.. Like what has been analysed
and found that it isinks abit, i think better change.
Thats just my point of view