When activating the latest version of the Admiror Gallery plugin in Joomla 3.5.8 running PHP v7.1, you get PHP compatibility errors.
Have you checked and validated the plugin code is PHP V7.1 compliant?
PS: It does not block the plugin from functioning, nor does it make Joomla send HTTP errors. So when not running in debug mode / max error reporting level, you will not notice the errors.
To be more precise, the error code you're getting is this one:
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; plgContentAdmirorGallery has a deprecated constructor in httpd.www/plugins/content/admirorgallery/admirorgallery.php on line 18
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