From the comment it seem that you are talking about CV cured cores. In mean peroxide cure cables, the relation is very critical in between the temperature and half life of peroxide.
When we using pre-heater, we are actually supplying heat internally or in other words we are keeping the material and external heat for activating the peroxide breakdown. As the process was activated but remained uncompleted due to insufficient heat sum because of pre-heater trip, you keep the insulated core in some hot environment or as it is for some days. You will find the improvement.
You can use degassing chambers for this purpose.