This message can be ignored as per this post https://community.ipfire.org/t/squid-web-proxy-started-with-2-errors/1085/2
This message suggests that there is an error in the squid.conf file. The entry for the access_log should read as
access_log stdio:/var/log/squid/access.log
The first line suggests that the conf file is set up to log to /dev/null.
What logging entry do you have in the /etc/squid/squid.conf file.
Do you have logging enabled on the Proxy WUI page.
The squid.conf file should not be manually edited as it is controlled by the data on the Proxy WUI page. If it has not been edited then possibly the squid.conf file has got corrupted or confused.
The simplest in that case would be to re-install.
This indicates that some form of buffer overflow occurred. As the program is compiled with the stack protector enabled then a stack smash detected causes the program to stop. Without that stack protection it would be likely that a segmentation fault in the kernel could occur.
Not sure if the logging error could cause the stack smash. I did find an entry about stack smashing related to stdio, as per the reference in your output from starting squid.
Maybe you could show a screenshot of your proxy WUI page and the squid.conf entries.