This affects users who use a different timezone then JIRA server starting with 2.11.7 - 08/March/17 release of the add-on.
For example if a user enters '17/May/17 10:30 AM' when his time-zone is set to GMT+7 and his server's timezone is GMT-3, there will be 10 hours difference. Work logs will be stored as if it is entered '17/May/17 10:30 AM' with jira server's timezone (GMT-3). To fix this you should subtract 10 hours from the recorded work log.
work logs are stored in 'worklog' table. startdate keeps the date on which work log is entered and it is the column you should update. For the above example you should extract 10 hours from the current value of the row.
Every database has a build-in function for manipulating date and time. Use this function to update existing records. You can use following examples once you identify the work logs you need to update.