I did wonder if the bottle was punctured, but doesn't the sealant coagulate in tyres when the escaping air pressure is forcing it out of a hole?
The bottle isn't pressurised though, so no pressure forcing it into any gaps. So you might just have had sealant slowly clumping over time as the liquid component dried out and the particles joined up.
@hippy started
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I did wonder if the bottle was punctured, but doesn't the sealant coagulate in tyres when the escaping air pressure is forcing it out of a hole?