Arrange the chicken thighs in the slow cooker so that they are not overlapping.
In a medium bowl, whisk together the honey, soy sauce, blackberry jam, hoisin, olive oil, garlic, onion, and crushed red pepper flakes, and then pour the sauce over the chicken. Cover the slow cooker and cook the chicken on LOW for 4 to 5 hours until the chicken is fully cooked.
Using tongs, remove the chicken from the slow cooker (reserving the liquids) and place it on a cutting board. Use two forks to shred the chicken into smaller pieces. Place the shredded chicken in a large serving bowl, set aside.
In a small bowl, whisk together the cornstarch with 3 tablespoons of cold water to make a slurry.
Transfer the liquids from the slow cooker into a small saucepan set over medium-high heat and whisk in the slurry. Bring the sauce to a boil and cook it until it reduces and has thickened slightly, about 3 minutes. Pour the sauce over the chicken, tossing to combine. Serve the chicken topped with sliced scallions and sesame seeds.