I think this is the cause not sure hw to fix
root@pihole:/var/log/lighttpd# nano error.log
bash: nano: command not found
root@pihole:/var/log/lighttpd# more error.log
2020-05-10 15:05:49: (log.c.217) server started
2020-05-11 20:16:56: (log.c.217) server started
2020-05-13 22:38:25: (log.c.217) server started
2020-05-14 11:26:35: (log.c.217) server started
2020-05-16 13:11:56: (log.c.217) server started
2020-05-16 13:28:42: (log.c.217) server started
2020-05-16 23:50:28: (mod_fastcgi.c.2543) FastCGI-stderr: PHP Warning: fopen(/etc/pihole/custom.list): failed to open stream: No such file or directory in /va