Weird output voltage on op amp triangle wave generator
Your integrator drifts. Possible reasons: Integrator opamp has offset voltage error or the  leftmost opamp produces non-symmetric pulses which have DC-component. Offset error can also be caused by opamp input current which causes voltage drop in a series resistor.
Integrator drifts finally to the + or minus voltage limit. Then it becomes non-linear and works unpredictably. In your case it seems to be able to somehow be reset after drifting to the edge.
Design your multivibrator so that the charged capacitor and its charging resistor are replaced by an integrator. If the integrator is a part of the oscillator loop it cannot drift to the non-linear range.