Odd Trackpad behavior with 2015 MBP, Mojave

Hello all. I'm a long time user and big of BTT. Over the years I've convinced a number of people to buy it. This is my first post.

I have very few actions which I've been using these on a 2012 MBP for years running Mojave, as I need to still use some 32-bit apps. I now have a 2015 MBP, also on Mojave, and running the same version of BTT, which is 3.312.

Two of my actions are a three finger swipe up to return to the top of page, and a three-finger swipe down to return to the bottom of a page or list. These are system-wide and app-wide actions. These actions never fail to work as intended on the 2012 Mac, but often do not on the 2015 Mac. Sometimes I have to swipe several times to go the top or bottom. Sometimes a three-finger swipe will only go a small distance, then a small distance again. Sometimes the actions don't work at all.

I have not felt the need to update BTT from 3.312 since I am not on Apple Silicon, still running Intel, and as stated these actions work perfectly on the 2012, MBP but not the 2015.

OOPS!, I nearly forgot two important points: oftentimes the odd behavior I've described is with Safari (version 12.1.2 (14607.3.9), and in a folder, such as the Downloads folder. In Chrome and Firefox the actions behave perfectly.

Any help appreciated.
Thank you.

Macbook Pro 2012 and Macbook Pro 2015
Both running last version of Mojave.
Using only built-in Trackpad
BTT 3.312
Note: the 2015 computer was restored from a Carbon Copy Cloner backup of the 2012 computer.