On Windows 10.
On starting Gnucash with some reports left active from previous session, progress shown on Splash window is normal until first report starts rendering. Then system appears to "hang" for about 30 seconds. Eventually the reports finish rendering and the program appears to start up and operate normally.

If I close all the reports out, and restart Gnucash, it appears to start up normally in the expected amount of time (a few seconds on my system). However, when I choose to run any report, custom or otherwise, the 30 second delay occurs, with the system appearing to hang. After the delay that report is rendered. Any other reports added then generate quickly as expected.

This behavior is new, within the last several days. I notice that on November 15 and 18th some auto-updates were applied to my windows system: KB4048954 (can be uninstalled) and KB4049011 (cannot be uninstalled). I have no other info on these updates. My recollection is that prior to this, Gnucash was rendering reports with no delay.

I also have a MacBook Pro with OS X High Sierra. The latest stable Gnucash works perfectly on this system, with the same reports and data files.

The prievious stable Gnucash, 2.4.15 works on the Windows 10 system with no delays in rendering reports. However the Add Report feature seems to be permanently grayed out, so I cannot save customize reports, or have not figured out how.

I have removed and reinstalled 2.6.18 to no benefit.

Hope this is not TMI, I have not reported bugs before.