Stop open blasting. Do some research and get yourself a closed loop if you still want to make BHO.
It is certainly possible to burn the oil, and if it were to decarb you wouldn’t be able to whip it. However, 40c isn’t really hot enough to darken product like that or decarb without a significant amount of time. Is it possible you’re heating the oil beyond what you think?
Pancake griddles and heat mats were pretty common with the old stock pot vacuum chambers. Used vacuum ovens are pretty cheap these days too.
Also, don’t blast or place the oil straight into the chamber, it should be in a jar/dish or on some parchment.