As found in T256449, atslog-backend spams the message Unable to read from socket to syslog if the relevant fifo-log-demux service hasn't started yet. We do already have a task for the purpose of explicitly specifying the dependency between atslog-backend/tls and their fifo-log-demux counterparts (T256467).
That being said, the spamming itself is caused by fifo-log-tailer retrying indefinitely and immediately to connect to the specified and non-existing unix socket:
root@cp4028:~# fifo-log-tailer -socket this-does-not-exist-at-all.socket 2020/11/27 10:46:22 Unable to read from socket: dial unix this-does-not-exist-at-all.socket: connect: no such file or directory 2020/11/27 10:46:22 Unable to read from socket: dial unix this-does-not-exist-at-all.socket: connect: no such file or directory 2020/11/27 10:46:22 Unable to read from socket: dial unix this-does-not-exist-at-all.socket: connect: no such file or directory 2020/11/27 10:46:22 Unable to read from socket: dial unix this-does-not-exist-at-all.socket: connect: no such file or directory [...]
We should make sure that fifo-log-demux retries connecting less aggressively, eventually giving up after a while.