As part of my aggressive and varied work history following USN retirement, sold windows and bath accessories to residential new construction builders. Tempered glass has a number of interesting qualities. Occasionally, as part of the tempering process, the glass will pick up nickel contamination which forms a stress point in the panel. At some point in its life, who knows when, why or what, conditions will exacerbate the stress point and the panel will spontaneously shatter. Uncommon, but not rare.
Don't know if that happened in your case, but, we had a local glass guy replace a panel in our shower that had decal adhesive that did not respond to any remover.
Cost a LOT less than $800. Spent more on various adhesive removers than the new panel cost.
Terry & Rosalina
2007 Winnebago Journey 34SE
Retired Navy Mustang & Navy Wife