Ad blue has an expiry date and has to be stored in very specific conditions. If not it will cause you problems.
It should not be stored in direct sunlight and should not be stored in temperatures exceeding 25C. Its all on the product label in small print.
If you see any crust or crystals around the lid of the ad blue bottle do not buy it or do not use it. You will have problems.
Buy the stuff fresh with at least 1 year on the expiry date and ensure it has been stored correctly. you wont have any issues then.