Benzotriazole isn't very soluble and 2% is perhaps at the limit of practicality. That said, if the solution's temperature gets below a certain threshold, then recrystallization occurs, which is what happened to your solution. You got some very nice benzotriazole crystals. You can warm it up and stir it to make it redissolve, but I'd further dilute it to twice its volume and make a 1% solution.
Sodium carbonate is hygroscopic and tends to absorb water from the atmosphere, but truth be told, I'm surprised that it got so ugly. I've seen other compounds becoming a soggy mess (ammonium nitrate), but stored in an open bag.