there is a question,Please help me !

Please open a support case with qkview and /var/log tar ball, to find the root cause. Are there any core files in /var/core directory? If so, when you open the case, upload the core and their corresponding md5 checksum as well.

Also is there any specific reason why you are still using 11.5.1-HF6? Because the latest maintenance release for the 11.5.x branch is 11.5.4. It has more than 500+ bug fixes compared to your current version. You may want to consider upgrading to 11.5.4.