Why is this exclude_lines in filebeat excluding all logs?

If you simplify your exclude_lines-configuration to the following, it will be matched by filebeat.

exclude_lines: ['\"PUT.*gitlab-ci-multi-runner']

I have read through the exclude_lines and the regexp-support documentation, but I didn't figure out the reason why your initial regexp does not match the three lines, since they match when I add it to regexr.com and choose PCRE as the regex engine.

If you want to find out what caused it to not be matched I would suggest that you remove one and one element from the regexp until it matches.

First remove the grouping

exclude_lines: ['.*\bPUT\b.*\bgitlab-ci-multi-runner.*']

Then try to remove the \b entries

exclude_lines: ['.*PUT.*gitlab-ci-multi-runner.*']

Then you should get to something similar to my answer.

exclude_lines: ['PUT.*gitlab-ci-multi-runner']

You can also remove one and one entry at a time, and not all \b elements. When you figure out which entry caused exclude_lines to not match, it will be much easier to find out why.

I hope this answer will help you along the way!