Hi.
First of all i don't think there was an agent update to 8.1.1 from 8.1. The installer is still 8.1.0-15876228 when i click download agent in loginsight 8.1.1 now I don't have an 8.1 enviroment to compare it to so I can't be sure.
Apparently the autoupdate feature is enabled in the agent by default so your uncommenting of the line auto update = yes had no effect according to this link. "Auto-update for agents is enabled by default. So, the default value for auto_update is "yes", even when commented."
https://docs.vmware.com/en/vRealize-Log-Insight/8.1/com.vmware.log-insight.agent.admin.doc/GUID-F2FF...
I don't think there is any force command other than maybe trying to disable then enable the enable auto update all agents switch. But the again it should have updated all agents if there where an update as the autoupdate on the agent is enabled until you specificaly uncomment it and set it to no.