The plugin does not exist.

I guess the error came from

micro_node.links.task.yml

micro_node.site.local_task:
  deriver: 'Drupal\micro_node\Plugin\Derivative\MicroNodeAddLocalTasks'
  base_route: entity.site.canonical
  weight: 100

You should debug MicroNodeAddLocalTasks(), I guess at a moment we have this plugin for a site (which generate a local task for the content type event) and for another site this content type is not enabled for being eligible for the local task. May be a cache issue or another thing. Let's me know your debug result.

I didn't notice anything unusual in the logs.
I had to comment all the code because it was crashing too often for a website with traffic.
The "event" content type is enabled for the site type & on the local task tab.

I didn't succeed in reproduce this issue. Would try this patch to see if this resolve the issue in your use case.

The last submitted patch, 4: 3359402-4.patch, failed testing. View results →
- codesniffer_fixes.patch Interdiff of automated coding standards fixes only.

This one should pass