Fatal error: Class ‘Traffic\System\SharedMemory’ not found in

Hello Dear Pierre,
when i am trying to activate the traffic plugin i get this error:
Fatal error: Uncaught Error: Class 'Traffic\System\SharedMemory' not found in /home/xxx/domains/freshuk.co.il/public_html/wp-content/plugins/wp-traffic-2.7.1/includes/features/class-memory.php:160 Stack trace: #0 /home/xxx/domains/freshuk.co.il/public_html/wp-content/plugins/decalog/includes/libraries/lock/mutex/LockMutex.php(48): Traffic\Plugin\Feature\Memory::Traffic\Plugin\Feature\{closure}() #1 /home/xxx/domains/freshuk.co.il/public_html/wp-content/plugins/wp-traffic-2.7.1/includes/features/class-memory.php(171): malkusch\lock\mutex\LockMutex->synchronized() #2 /home/xxx/domains/freshuk.co.il/public_html/wp-content/plugins/wp-traffic-2.7.1/includes/features/class-memory.php(114): Traffic\Plugin\Feature\Memory::write_records_to_memory() #3 /home/xxx/domains/freshuk.co.il/public_html/wp-includes/class-wp-hook.php(305): Traffic\Plugin\Feature\Memory::write() #4 /home/xxx/domains/freshuk.co.il/public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters() #5 /home/xxx/domains/f in /home/xxx/domains/freshuk.co.il/public_html/wp-content/plugins/wp-traffic-2.7.1/includes/features/class-memory.php on line 160

any clue what should be done?
thank you !