I hope that's the right place to fill a bug report. There's not really any information about that on https://www.collaboraoffice.com/code/ . anyway. In the current code debian package version 4.2.0-2 there is a problem with logging. When setting <logging> <file enable="true"> ... to activate the logging, loolwsd is unable to write to /var/log/loolwsd.log. It is necessary to create the file manually and chown it to lool
I don't think it's a bug. loolwsd runs under the restricted user 'lool' by design.
Most other daemons also run with their own user, but still manage to write to /var/log (I don't know if they use the installed syslog daemon for that or something similar). Anyway, usually if a package has a default log path in it's configuration file the user expects it to work, when he uncomments that path. If it doesn't work by purpose, at least make a comment in the configuration file. (If he does that, there are already other things which aren't working, and believe me, it doesn't improve the mood when logging fails ;-))