Fatal error: Allowed memory size of 71303168 bytes exhausted

What is the root cause of the error bellow and how do I solve it permanently?

I've been increasing memory. It goes away for a while and then it comes back again.

Thanks

Fatal error: Allowed memory size of 71303168 bytes exhausted (tried to allocate 30720 bytes) in /home/onlinele/public_html/wp-includes/class-simplepie.php on line 2723