(Cache::lock()) -> get() -- Under what conditions does it return false?

PHP Snippet 1:

Log::info('checkpoint 2 ' .  $lock->owner() . " - get? " . ($lock->get() ? "true" : "false") );
Log::info('checkpoint 2A ' .  $lock->owner() . " - get? " . ($lock->get() ? "true" : "false") );

PHP Snippet 2:

[2022-05-12 22:41:11] production.INFO: checkpoint 2 l5qJhOOORy1nNFHt - get? true
[2022-05-12 22:41:11] production.INFO: checkpoint 2A l5qJhOOORy1nNFHt - get? false