Issue is still an issue however we found that it is related to forking the laravel process.

We found that the attached test breaks if you take out the call to Cache::getStore()->getRedis()->purge(); So we started running reconnecting to redis after each fork and on the main thread, but we are still seeing the issue intermittently.

---------------------- UNIT TEST -------------------

/**
 * @test
 */
public function break_redis_cache()
{
    DB::reconnect('main');
    DB::reconnect('tenant');
    for ($i = 0; $i < 10; ++$i) {
        $pid = pcntl_fork();
        if ($pid) {
            if ($pid < 0) {
                throw new IndexingException('Failed to fork during Elastic indexing.');
            }

            $pids[$pid] = $pid;
        } else {
            DB::reconnect('main');
            DB::reconnect('tenant');
            Cache::getStore()->getRedis()->purge();
            for ($j = 0; $j < 20; ++$j) {
                $sleep = random_int(0, 15);
                usleep($sleep);
                Cache::tags(CacheTags::ELASTICSEARCH_REFRESH_REQUIRED)->add('logs', 1, 60);
            }
            exit();
        }
    }

    while (count($pids) > 0) {
        usleep(300);
        foreach ($pids as $pid) {
            $res = pcntl_waitpid($pid, $status, WNOHANG);
            if ($res === -1 || $res > 0) {
                unset($pids[$pid]);
            }
        }
    }

    $this->assertTrue(true);
}