I notice cracks in my window, how is this possible?

Cracks on acrylic-glass component parts can be caused by so called “stress corrosion”.

Stress corrosion cracking is a chemical and/or electro-chemical corrosion of the material under simultaneous influence of a corrosion agent and static tensile stress.

During the usage-/lifetime time of the window, so-called skin stresses can be formed on the surfaces caused by temperature and wet/dry alternations. These are completely harmless and over many years
usage time, supposing regular and appropriate cleaning and maintenance has been done) also do not result in damage. However, if cleaning and care agents (corrosion agents) unsuitable for acrylic glass are applied, they will attack the window material which in final stage can lead to the destruction of the pane.

THEREFORE: NEVER use aggressive cleaning agents such as glass cleaners, all-purpose cleaners, abrasives, or washing-up liquid. Also, never use alcohol-containing cleaning agents.