Smush Options Panel is not loading

When I go to my site Dashboard > Smush Pro, it takes long, and then finally server returns 504 error. I am hosted in Google Cloud. After adding the WP Debug variables, I don’t see any debug.log file inside the wp-content directory. For I found the following from another log in the server:

02T03:11:41+00:00 CRITICAL Allowed memory size of 134217728 bytes exhausted (tried to allocate 8388616 bytes)

2018-10-02T07:40:54+00:00 CRITICAL Allowed memory size of 134217728 bytes exhausted (tried to allocate 8388616 bytes)

I am not sure if this is happening with Smush Pro, but I can’t think of any other reason. Currently I have 256MB memory limit. Can you help me to run Smush Pro within this limit?