Opening the calendar for the start and end dates displays the wrong initial calendar.
If today's date is 23rd April 2018 then the Calendar shows 18th April 2023. i.e. the day and year have been swapped
This is Jira problem: https://jira.atlassian.com/browse/JRASERVER-62857, please see it for possible workaround, and comment/vote on it to get traction and watch it for possible fix.
Note, the issue does not appear to happen with Chromium, but only with Firefox apparently.