Apple devices with jammed registration button (not responsive)

[TheGrandVizier]

On some devices, particularly 6s and 5s, registration button gets frozen and cannot be pressed.

Reproduce:

1. in browser, navigate to idftrees.bh.org.il
2. fill out the registration form
3. press "register"

Expected result:
Receive confirmation SMS code

Actual result:
button not responsive, stuck on registration screen

iPhone 6s fails to press the register button or fails to respond to it.
iPhone 5s behaves the same.
iPad 4 Retina behaves the same.

I will add affected devices to this list as i find them. So far I think it is safe to assume the "S" models as well as the newer iPads being the problematic ones.

UPDATE 22/03/2016: All tests executed on latest iOS (9.2.1), safari browser.

This is a remote debug output from the subject iphone.

"Error: undefined is not an object (evaluating 'angular.fromJson(localStorage.model).me')
sendSMS@http://staging_idftrees.bh.org.il/modules/gt.app/services/registration.js:60:72
sendSMS@http://staging_idftrees.bh.org.il/modules/gt.app/services/registration.js:108:50
register@http://staging_idftrees.bh.org.il/modules/gt.app/views/register.js:10:31
http://staging_idftrees.bh.org.il/lib/angular/angular.js:10943:26
http://staging_idftrees.bh.org.il/lib/angular-touch/angular-touch.js:441:21
$eval@http://staging_idftrees.bh.org.il/lib/angular/angular.js:12851:28
$apply@http://staging_idftrees.bh.org.il/lib/angular/angular.js:12949:28
http://staging_idftrees.bh.org.il/lib/angular-touch/angular-touch.js:440:19
dispatch@http://staging_idftrees.bh.org.il/lib/jquery/dist/jquery.js:4732:32
handle@http://staging_idftrees.bh.org.il/lib/jquery/dist/jquery.js:4544:33"

[TheGrandVizier]

iPhone 6s - Passed
iPhone 5s - Failed
iPad 4 Retina - Device was not available.

[TheGrandVizier]

Ran another set of tests (again) on Keynote's Device Anywhere.
iPhone 6s - Failed
iPhone 5s - Failed
iPad 4 Retina - Failed