For some reason, on a few of our Jenkins servers, the Slack 1.7 plugin fails to post messages to the slack channel. We have had to revert to version 1.2 of the plugin. In comparing the project configs and the console logs, there is no apparent reason for this. This is with projects we have imported onto these machines from older machines. New projects created after the 1.7 plugin was installed seem to post just fine.

The new machines are all behind a proxy server. Not sure if that makes a difference. However, since newly created jobs seem to use the Slack 1.7 plugin just fine, it is probably a red herring.

I'm happy to collect debug data if you can provide any suggestions for doing so.