Ninjaforms get stuck on “Processing” after activating this plugin

Hello,

After a NinjaForm form is submitted on my website the submit button gets stuck on “Processing…” and I get the following errors:

TypeError: Cannot read property ‘nonce’ of undefined
at i.submitErrors (front-end.js?ver=3.4.22:2)
at p (backbone.min.js?ver=1.4.0:1)
at f (backbone.min.js?ver=1.4.0:1)
at l (backbone.min.js?ver=1.4.0:1)
at u.Channel.n.trigger (backbone.min.js?ver=1.4.0:1)
at Object.success (front-end.js?ver=3.4.22:3)
at i (jquery.js?ver=1.12.4-wp:2)
at Object.fireWith [as resolveWith] (jquery.js?ver=1.12.4-wp:2)
at x (jquery.js?ver=1.12.4-wp:4)
at XMLHttpRequest.c (jquery.js?ver=1.12.4-wp:4)

front-end.js?ver=3.4.22:3 Parse Error
front-end.js?ver=3.4.22:3 TypeError: Cannot read property ‘nonce’ of undefined
at i.submitErrors (front-end.js?ver=3.4.22:2)
at p (backbone.min.js?ver=1.4.0:1)
at f (backbone.min.js?ver=1.4.0:1)
at l (backbone.min.js?ver=1.4.0:1)
at u.Channel.n.trigger (backbone.min.js?ver=1.4.0:1)
at Object.success (front-end.js?ver=3.4.22:3)
at i (jquery.js?ver=1.12.4-wp:2)
at Object.fireWith [as resolveWith] (jquery.js?ver=1.12.4-wp:2)
at x (jquery.js?ver=1.12.4-wp:4)
at XMLHttpRequest.c (jquery.js?ver=1.12.4-wp:4)

However, after disabling this plugin I don’t get the error anylonger. Any thoughts how to fix this?

Thanks!