I know things dissolve quicker in hotter solvents but I was wondering if there existed an exception to the rule. If not water, then what about other solvents and/or non-solid solutes?
Just one example is Poloxamer 407 which forms a hydrogel at room temperature at sufficiently high concentration. Adding solid Poloxamer 407 to water at room temperature would easily result in Poloxamer 407 powder encapsulated in gel which would strongly slow down the dissolution process. At a colder temperature, such as 4 °C, the gel does not form, so dissolution is typically achieved in a shorter time.
So yes, there are examples of compounds that dissolve faster in colder conditions. As usual when it comes to kinetics, the mechanism is highly relevant.