Hi,
Thanks for reaching us!
Sorry for the late response!
Please make sure that you have installed the last version of the Cost Calculator Builder (2.0.4).
The main point to mention is that mostly the error when calculators are not being saved 100% caused by one of the plugins activated on your website. So, please deactivate other plugins except for Cost Calculator and use our plugin purely. After that, activate the side plugins one by one, to find which one exactly is affecting. If the problem remains the same even after all side plugins are deactivated then please try to switch the active theme to the default one.
Regards