Cannot add display rules

[JessChampion]

Each time I click the add button to add a display rule I get the following error:

Uncaught TypeError: this.getGridField is not a function
    at a.fn.init.onclick (GridFieldExtensions.js?m=1526356267:206)
    at one (jquery.entwine-dist.js?m=1520903238:1011)
    at HTMLDocument.prxy (jquery.entwine-dist.js?m=1520903238:1504)
    at HTMLDocument.dispatch (jquery-1.7.2.min.js:3)
    at HTMLDocument.i (jquery-1.7.2.min.js:3)

Required Versions in Composer:
"silverstripe/recipe-cms": "^1",
"silverstripe/userforms": "^5.1",
"dnadesign/silverstripe-elemental": "^2.1.0",
"dnadesign/silverstripe-elemental-userforms": "^1.0@dev",

Installed version of GridFieldExtensions 3.1.1
Have tried nuking the vendor folder, clearing the composer cache and reinstalling, still get the same issue.

Please let me know If i can provide any more information

[robbieaverill]

Thanks for reporting! This issue has cropped up a couple of times - the closest I can find at a glance to reference is symbiote/silverstripe-gridfieldextensions#246, so I'll close this as a duplicate of that. Our team is looking at these issues today =)