Webfront connection lost / unexpected token n

After updating to # 3346 or newer beta version I got the following message on IE, Chrome and Android device (connection lost. Syntax error Unexpected Token N) When you run the page I have an automatic restart after a few seconds.
How to solve this problem?



Did this error appear before? From which version did you update?


As I remember the problem was start with the beta version of the end of January.