Google Analytics is starting a new session after each PayPal payment

I’m trying to get PayPal and Google Analytics to play nicely.

I have followed all the PayPal setup instructions here: https://docs.woocommerce.com/document/paypal-standard/

And I have Google Analytics setup correctly on all my pages.

I then do test transactions using the Google Tag Assistant extension. You can go through the checkout process like any customer would and it records the tracking code at each step and provides warnings for any potential tracking issues.

The warning message I am seeing is this, right after the customer returns from PayPal:

“This hit starts a new session, most likely because the campaign changed”

It means two sessions are being recorded. One session which tracks the user up until they click the Checkout With PayPal button, and then another session starts once they come back to my site from PayPal after the payment is complete.

How do I fix this so it is recorded as just one session?

I have included ?utm_nooverride=1 on the end of my PayPal auto return URL but it does not help.