I noticed that after upgrading to 3.0.2. yesterday I got an error message from scheduled tasks with this content: plugins.generic.usageStats.pluginNotEnabled
So after looking at the settings I noticed that in all journals the plugin has been disabled.
The same here. Here is the error from the log:
[2017-02-04 22:05:40] [Notice] Task process started.
[2017-02-04 22:05:40] [Warning] Usage statistics plugin is disabled. No log files processed.
[2017-02-04 22:05:40] [Notice] Task process stopped.
I had to enable it for each journal one by one. But I am still not sure if it works at all. Since we do not have any statistics in the metrics table since the end of 2016 
Now I am experimenting by enabling the Acron plugin for one of our journals. But I still do not see any changes. Please, help!
I think in our case this was fixed simply by enabling it in all journals.
I can confirm this later, but it sounds like there is some other problem there in your case. Maybe with scheduled tasks
How did you enable the UsageStats plugin? I’m getting the same error.
Settings => Website => Plugins => Usage Statistics
Check the checkbox
Funny, I don’t see that option. 
Do you mean that there is no Usage Statistics plugin in the plugin listing?
Yes, there is no plugin named Usage Statistics Plugin in the list. Pretty weird because I’ve upgraded to OJS 3.0.2 
Is your installation working correctly otherwise? Can you access your server via ftp and check if the plugin folder is there?
Everything else is working fine, yes there is plugin folder with generic/usageStats and generic/usageEvents directories in it.
and that is in lib/pkp/generic ?
Yes, it is there in lib/pkp/plugins/generic and the root (public_html) directory’s plugins folder
What I would probably do is run the upgrade script again and see if the plugin gets registered. I mean php tools/upgrade.php upgrade. But to be in to save side you could do a backup before that.
edit: but I really do not know why an existing plugin is not visible there. You could double check that the folders contain all the correct files
Will try tomorrow and update here 
I mean you could also check before doing the upgrade that all the files visible here ojs/plugins/generic/usageStats at ojs-stable-3_0_2 · pkp/ojs · GitHub and here pkp-lib/plugins/generic/usageStats at ojs-stable-3_0_2 · pkp/pkp-lib · GitHub are also in your installation.
Yes, all the files are there in the folder, I’m not sure why the plugin wouldn’t show up despite being the existing one. I will backup and upgrade again to see whether it solves the problem or not. Thanks
Okay, so all of a sudden, everything is showing up in my admin panel. I didn’t do upgrade, it showed up on its own.
Maybe I changed something without noticing and hence it started working again. I enabled the usageStats plugin and it is working.
Thank you for the help. 