vapor temp swings and bursts

[bigbatch]

I use a bain marie heated pot still for both both stripping and spirit runs. Lately on my spirit runs, I have been having an issue with extreme temperature fluctuation as measured by my vapor probe. I will get product to begin coming off at about 80 C, then it will stop as the temperature drops to 76C, then there will be a big burst of vapor and product come through the condenser that is extremely hot as the vapor probe jumps to 83-85C. It will repeat this process for more than hour until it seems to equalize. Not sure what is going on as the the temperature of the water I am pumping through the jacket to heat the low wines remains constant.
What I've tried:
1) Keep the agitator on low instead off to break the surface tension
2) Keep the jacket temp really low so that it heats up slower.
3) Keep the jacket temp really high so that it heats up faster.
4) Add water to the low wines so I have a full pot rather than a half pot
5) Wear my shirt backward and hop up and down three times before turning on the still
None of these seem to make a difference. Neither do the type of low wines, happens with fruit and grain spirit runs alike.
Thoughts?