Thank you for reporting this. I will have to investigate it. I will gat back to you. How did you narrow it down to these two plugins?
The conflict is between SEO Yoast and Google Site Maps. Whenever any plugin is activated, Yoast SEO checks for conflicts between itself and a hardcoded list of plugins (in wordpress-seo/admin/class-plugin-conflict.php). Easy AdSense is not in that list, but site map generating plugins are. Just that the conflict message is triggered when Easy AdSense is re-activated after updating. The same message will show up if you re-activate any other plugin (including Hello Dolly).
After updating the plugin, it may take a minute before WordPress confirms that it has been re-activated. You may have left the window before that message came up, which may be why the plugin was not activated.
I will close this issue as resolved. Please reopen it if you sill have questions about it.
