This is a general laboratory issue.
Safe ways of separating stuck joints are soaking the joints, using a sonicator / ultrasonic cleaner, using a solvent to dissolve chemical residue, or applying heat. You should not use force (e.g. do not try to loosen the joint by knocking the glassware on the edge of the bench), because this is likely to lead to breakage, and is unsafe.
Some chemists grease glass joints to act against joints sticking, if this is suitable for their chemistry/application.
Here at Radleys, we tend to use Rodaviss joints (the red cap and screw thread etc.), because their special design makes it easier to separate joints compared to standard ground glass joints.
The wide neck flask design we offer as an option for the Carousel 6 Plus and Tornado uses a flat flange rather than a glass joint, so that also helps prevent this issue.
Please note, glass is relatively fragile (even laboratory borosilicate glass 3.3), and is not covered by warranty.