Magento stores all schedules in table in GMT time. When Magento tries to schedule new job and add it in table, this method \Magento\Cron\Model\Schedule::trySchedule convert time according to server timezone and compares with schedule specified in your crontab.xml. During schedule executions Magento converts time from table using server timezone as well and compares it with current server time.
So it isn't the issue. There are always all schedues in table in gmt.