Macbook Pro trackpad gone weird

Hope you've resolved it by now, but if not, I figured out my double-click/drag problem. For some reason the update changed default trackpad settings in System Preferences Accessibility. I had to enable dragging to without drag lock. Weird.

Just in case there are other factors in play, read this Apple document and carefully check the environment.

https://support.apple.com/en-gb/HT201542

You could also reset the SMC. https://support.apple.com/en-gb/HT201295

According to this article : If your pointer is jumpy when you use a trackpad, Magic Trackpad, or Magic Mouse - Apple Support

If your pointer is jumpy when you use a trackpad, Magic Trackpad, or Magic Mouse

Learn what to do if your pointer jumps, moves unexpectedly, or acts erratically when you use an input device with a touch surface, such as a Mac notebook trackpad, Magic Trackpad, or Magic Mouse.

Try these tips to resolve the issue:

Check your device's power

Make sure your device's batteries aren't low. If you're using Magic Trackpad 2 or Magic Mouse 2, make sure its rechargeable battery is fully charged.

Avoid accidental multiple touches on the surface

Be sure only one part of your finger is touching the touch surface and that you're not resting your wrist on or very close to the surface. The touch surface might interpret this as your finger touching it and move the pointer in that direction.

Keep touch surface dry and clean

Moisture collecting on the touch surface can also cause this issue. Wiping off the surface of the trackpad or mouse with a cloth or tissue usually fixes this.

If the issue goes away when you put a piece of paper between your finger and the touch surface, consider purchasing a Teflon applique to fit over the surface to prevent moisture from having direct contact with the touch surface. Before you install the Teflon applique, make sure the touch surface is clean and dry.

Note that oil or lotion can also cause the same issue. You can clean your device's touch surface with a lint-free cloth lightly moistened with water.

Remove jewelry

Jewelry might also cause interference when you use a device with a touch surface. Try removing rings or bracelets and see whether the jumpy or erratic behavior disappears.

Check the power adapter you're using with your Mac

This behavior might happen if you use a power adapter made by a third-party company.

If you're using one of these power adapters, unplug it and try running your Mac from battery power to see whether the pointer behaves correctly. If the device behaves normally while running from the battery, there might be an issue with your power adapter.

Avoid wireless interference

Bluetooth devices can act erratically when there's wireless interference. See Wi-Fi and Bluetooth: Potential sources of wireless interference for more information.

Start your Mac in Safe Mode

If none of the above resolves the issue, you can start in Safe Mode to rule out third-party software as a cause.

Restart the computer holding down the command - option/alt - P - R keys before the gray screen appears. Continue to hold until you hear the startup chime for the second time.

Reset NVRAM/PRAM

Try running this program in your normal account, then copy and paste the output in a reply. The program was created by etresoft, a frequent contributor. Please use copy and paste as screen shots can be hard to read. On the screen with Options, please open Options and check the bottom 2 boxes before running. Click “Share Report” button in the toolbar, select “Copy Report” and then paste into a reply. This will show what is running on your computer. No personal information is shown.

Etrecheck – System Information

One other relevant Article is this one.

https://support.apple.com/en-gb/HT204621

Would I be right to assume you are running El Capitan or Sierra and do not have a Magic mouse connected at the same time