are you planning on a new site with Store Locator Plus so the site link you provided is it a staging site?
The Home page : https://www.postpullers.co.uk/hire/ shows that you have another Locator plugin installed. When you say the old store locator and gravity forms worked on the same page are you referring to store_locator_ word press? (That is a different plugin) not ours) I see on the home page link /hire tab the store_ locator _wordpress plugin is installed and not Store Locator plus , yet on your test page example link you provided above it has SLP. Just wanted to clarify because I saw a console error about sensor not required which indicated you are using another Locator plugin (SLP does not give you that error warning) so I checked the WP sources.
Having multiple Locator (conflicting) plugins can break the SLP map and geocoding so I do not know what it will do as far as conflicts with any of the add-ons. So it is possible there are other issues with your site and they are not relative to Gravity forms. I do not see where you have provided your Plugin environment. We always need that information (see Posting Guidelines) in order to provide you with answers that are pertinent to your particular issues.