It seems that the backspace key is being trapped in email fields, and its action is not permitted, hence one can't erase characters that have been entered incorrectly.
I have a form on this page with an email field: hidden link
To reproduce:
1. Into the email field type "john@.toolset.com"
2. Press backspace to remove all characters after the @
Hello. Thank you for contacting the Toolset support.
I just checked with my test site where I've added two email fields: "Business Email" and "emp-personal-email" and I do not able to reproduce this issue. The email field with backspace key works as expected:
=> hidden link
Then, I checked on your install and I can confirm that the issue with the problem URL you shared I can experience and backspace key is not working with email field as you described with the following link:
=> hidden link
When I checked the page source I can see there is JS error coming from your cache file:
It seems you are using third-party plugin that is minify the JS and that cases the issue. Can you please test by disabling that "autoptimize" plugin for now and check if that help you to resolve your issue. If that works, that there is issue when "autoptimize" plugin minify the jaavascript.
Ok great - I can confirm now I do not see the JS error on the browser's console but still the backspace with email field is not working.
As I shared with my test site as a proof that with minimum installation where only Toolset plugins active the email field with backspace works as expected.
In order to minimise the cause of the issue as well as to ensure there is no conflict between third-party plugins you are using or themes, we need to ran a test by disabling plugins one by one.
Could you please try to resolve your issue by deactivating all third-party plugins as well as the default theme to check for any possible conflicts with any of the plugins or themes? - Do you see any difference? If no:
I will require duplicator copy of your install to troubleshoot the issue further.