Problem first spotted 8th Sept 2016 after months of perfect operation…
category “archive” is used when posts are no longer current on the site, and all the “display-posts” statements include something like:
tax_2_operator=”category” tax_2_term=”archive” tax_2_operator=”NOT IN”
These statements are now being ignored so archived material is being displayed again. This only applies on posts and pages – all the widgets are still working properly.
Not yet referred to wordpress.
FIXED AUGUST 2017 – the issue was being caused by a single rogue “curly speech mark” in the code which was being generated in Word. Solution is to switch off curly speech marks in Word and remove them from the affected pages.