Current version 15.1
Did not have this issue with previous version, produced 2 reports within a month one before the update and one after. The first one went out fine, the second one have the following glitch:

• All pages have ONE master page footer including ONE variable connected to a header style - simple and standard, never caused an issue since the beginning of the function's history .

What happens in the spread:
Page 1 contains Header 1 and footer refers to H1
Page 2 contains Header 2 and footer refers to H2
Page 3 contains no header and footer (SUDDENLY!) refers to H1

And so on, the variable just falls back to the previous Header at random. Sometimes it's fine, sometimes it's REALLY NOT!

Got this fixed just now, by duplicating text-boxes with headers and deleting old ones, just purely duplicating over... So there were no issue with Variable - style connection, it's just loosing it all of a sudden...

So a heads up for everyone to be aware of it and watch it as I've already have a company's sustainability report stuffed up because of it, thanks Adobe, will you cover the cost of the reprint?