Need Support for unistim Channel

we have 60+ nortel phones connected to asterisk using unistim. asterisk is crashing frequently stating “segfault at 40 ip 00007f212bee923d sp 00007f20d3f06970 error 4 in[7f212becf000+22000]”.
i tried the below asterisk version.
1.8 => crashes rarely(but having problem in dial method).
11.12.0 => crashes twice or thrice in a day.(no other problem)
12.5.0 => crashes frequently.
Please suggest me any version with stable unistim support.
Thanks in advance.