Thermal Stress Cracking During Heat-Up on Glass Heated Bed
The problem is in the design of your bed. Let's start from the basic setup of a glass bed:

The heater element is usually mounted to a metal carrier, which is both spreading the thermal energy over the bed, but also is the structural element that is leveled against the carriage. Atop that comes the glass print surface.

Now, once the heater element is turned on, the aluminium starts to expand and evens the distribution to the glass. As the glass has a much lower thermal expansion coefficient, it doesn't expand as fast. Because of this, the glass surface should never be glued to the bed or heater but held in position to the metal bed with a clip. This way the thermal and mechanical stress on the glass sheet is mitigated: The metal bed evens the heat transfer and the clip can move its position on the glass.