Leads conversion window does not open when clicking convert Lead

[phongkni]

Please help me to solve this problem
If i click Convert Lead from the local network, there is no problem, only this problem when using an external network
When using DevTools in chrome (Ctrl + Shift + I), I see the following error message:

Failed to load resource: net::ERR_EMPTY_RESPONSE
send @ csrf-magic.js:52
send @ jquery.js:4
ajax @ jquery.js:4
callConvertLeadDiv @ Leads.js:235
(anonymous) @ VM905:1

file csrf-magic.js error code here:
return this.csrf_send(prepend + data);

Please help me
Thanks you