Telephone calls disconnecting issue

I have the users complaining that their telephone calls keep disconnecting in the middle of a call frequently. When I check the logs, I find these lines. How can I solve this issue?
This is after I gave the command tail /var/log/asterisk/full.

May 13 18:38:59 NOTICE[32187] cdr.c: CDR on channel ‘SIP/200-b7507ec8’ not posted
May 13 18:38:59 NOTICE[32187] cdr.c: CDR on channel ‘SIP/200-b7507ec8’ lacks end
May 13 18:40:15 NOTICE[32215] cdr.c: CDR on channel ‘Zap/3-1’ not posted
May 13 18:40:15 NOTICE[32215] cdr.c: CDR on channel ‘Zap/3-1’ lacks end
May 13 18:41:40 NOTICE[32222] cdr.c: CDR on channel ‘SIP/200-b7507ec8’ not posted
May 13 18:41:40 NOTICE[32222] cdr.c: CDR on channel ‘SIP/200-b7507ec8’ lacks end
May 13 18:58:29 NOTICE[32362] cdr.c: CDR on channel ‘IAX2/111-4’ not posted
May 13 18:58:29 NOTICE[32362] cdr.c: CDR on channel ‘IAX2/111-4’ lacks end
May 13 19:03:33 NOTICE[32440] cdr.c: CDR on channel ‘SIP/301-b7507ec8’ not posted
May 13 19:03:33 NOTICE[32440] cdr.c: CDR on channel ‘SIP/301-b7507ec8’ lacks end

need many more details. It’s like I took my car to the service center and they said the valve is not working correctly.

Please provide version of asterisk, FreePBX, trunk setup’s, phone type, version and setup being used.

There are currently about 10 places I can think of where the problem might be.