Maintaining Mash Temperature with Brewers Edge Mash and Boil

I bought a Brewers Edge Mash and Boil at the beginning of this year and for the most part, have been pretty happy (have used it 20+ times already).

One thing I continue to have issues with however is hitting my target OG, I think I'm coming way under. The only factor in the process that I don't think is occurring consistently is the mash as I notice the equipment wildly fluctuates in temperature during that process vs maintaining a steady temperature.

I've tried to address this by adding frequent recirculations and temperature measurements to the process and I'm likely going to set up a pump for future brews. But even with that, I still notice at times that the temperature has dropped to low-140s or increased to high-150s.

It's to the point where I'm considering going back to a sealed mash tun approach where I never had this issue before. Wondering if anyone has dealt with something similar and has any advice before doing that though.