There is no regression with the fix that we done in the 3.0.3 "Fix an ajax conflict with WooCommerce Tree Table Rate Shipping and HubSpot All-In-One Marketing" #803. It doesn't break the registration and the connection with the hubspot plugin.
As a reminder here is how to test Hubspot:

1. create an account on https://www.hubspot.fr/
2. go to Dashboard > Plugins > activated Polylang and HubSpot All-In-One Marketing - Forms, Popups, Live Chat
3. go to Dashboard > Hubspot > User guide > select your account > click on "Continue with this account" > you get "Your website is now connected to hubspot" as shown below
   
   and no more a 400 bad request in the console as shown here:
   

As a reminder here is how to test WooCommerce Tree Table Rate Shipping: (ticket HS)

1. go to Dashboard > Plugins > activated Polylang and WooCommerce Tree Table Rate Shipping
2. go to Dashboard > WooCommerce > Settings > Shipping tab > Tree Table rate > click on "Start from scratch", then "Add rule" > "Save changes".
3. check the console > the added 'pll_ajax_backend=1' no longer prevent WooCommerce Tree Table Rate Shipping from working.

This PR fixes as expected the issue reported on HS #14681 ticket (private) with the FS License Manager (version 4.3.5). As a reminder here are the steps:

1. go to Dashboard > Plugins > activated Polylang, Polylang for WooCommerce, WooCommerce and FS License Manager.

2. go to Dashboard > License manager > Import > Import Image License Keys From .zip File > upload a .zip file containing an image.
   

3. check the console > you shouldn't no longer get the error below: