I didn't realize why my test site is able to crash the different browsers.
The problem is quite limited on my iMac mid 2011 Sierra,
but on my iPad Air and on iPhone SE is very frequent.
Is a coding problem ?
Below the site and the credentials, if someone want to test.
Pratically when you Login or SignUp, it compare the email user (stored in Member collection by SignUp) with another collection where I stored all the potential Users that can SignUp with possibility to get documents, only them, by Wix Dropbox applet.