Reports very slow to open

[Christopher Stubbs]

Like Ron Burek (7 Jan 2018) I am running Gnucash 2.6.19 on Windows 10 pro, fully updated.
When you try to open any report, transaction report, profit & loss etc, Gnucash goes into a long time wait mode with the blank report tab open, typically about 3 or 4 minutes, before the report actually opens. Once you have any report open then running another one is no problem.
If you try to do anything else in Gnucash while you are waiting for the report to open you get the message "Gnucash is not responding" in the top ribbon and everything greys out.
This is all totally reproducible every time, not just occasionally.
This seems to have started to happen with 2.6.19 and the latest Windows 10 update (KB4056892 in early January). I don't know if this is just coincidence.
Anybody got any ideas about a fix?

Thanks

Chris Stubbs