There seems to be more to the problem than just the header.
1) Mouse hovering over the recall button no longer shows the return time of fleets
2) See attached screenshot....
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this is the detailed information of one of my flights. Similar results obtained when trying to determine the holding time of pirate fleets (screenshot also attached)
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Pressing F5 did not solve the issue. Manually clearing cache did not help either. Nor did rebooting the browser AND the computer.
Header still says "Undefined", fleet information detail still "undefined" and return times are not available...