Hello,
within the Release notes for EX Series 12.3R5, I can find the following:
On EX Series switches, the messages CMLC: connection in progress for long and pfem:devrt_gencfg_rtsock_msg_handler Incorrect major_type 8
might be displayed, but the messages do not impact switch functionality. [PR/890633: This issue has been resolved.]
Are you using an EX Switch with a JUNOS release older than 12.3R5?