PHP Warnings “failed to read session data: memcache”

Plugin v.4.6.0 PHP 7.1
Have a lot of warnings:
PHP Warning: session_start(): Failed to read session data: memcache (path: tcp://localhost:11211) in .../wp-content/plugins/shortpixel-image-optimiser/class/wp-short-pixel.php on line 21" while reading response header from upstream

After enabled this line in wp-shortpixel.php
define('SHORTPIXEL_DEBUG', true);

got also in my error.log:

PHP message: INIT: Session queue not found, updated from Options with []
PHP message: QUEUE: processing(): get:[]
PHP message: CHECK QUOTA: Skipped: """
PHP message: INIT: Session queue not found, updated from Options with []" while reading response header from upstream..