Try to build your Simulink model by using one of the following solvers instead of the default "ode3 (Bogacki-Shampine)" solver -
1. ode8 (Dormand-Prince RK8(7))
2. ode5 (Dormand-Prince)
3. ode2 (Heun)
4. ode1 (Euler)
This should fix the issue. You can change the solver by opening the Configuration Parameters (Ctrl+E) and then changing the 'Solver' under the 'Solver options' menu.