The only change in BatchPreprocessing 1.43 is a new
Save process log option, which is enabled by default. This option simply creates a plain text file with the log of the process. You can try with this option disabled, but this action, by itself, cannot slow down anything under normal working conditions (if writing to a plain text file slows down your machine, then there's a serious problem that has nothing to do with PI).
The PixInsight core application that you are using has not changed since December 2015. The latest build 1199, in case you are using it, has not changed anything significant except being compatible with new macOS 10.12 Sierra installations.
There must be something in your machine, other than PixInsight, that has changed in a way that affects its performance adversely.
I have resorted to deep sky stacker - which works fine on my windows 10 machine
Problem solved then!