Problem with AMP plugin php fatal errors

Hi, Currently we are having issues with the AMP plugin as we are using AMP version 0.7.1 in our wordpress version 4.9.6 and we are getting php fatal errors which is causing 500 errors and website is down. We are getting following php errors in log file

PHP Fatal error: Cannot redeclare class AMP_Rule_Spec in \wp-content\plugins\amp\includes\sanitizers\class-amp-rule-spec.php on line 13

PHP Fatal error: Call to undefined function is_single() in \wp-content\themes\arre\amp\single.php on line 2

Can you please help in understanding this errors in AMP plugin and why this are getting triggered in some particular time?