I noticed this morning at 9.05 after the hourly reset that images and files coming from the master site were not appearing, causing a large number of error messages such as below. 

At 10.05 after the next reset, the site displayed correctly. However, at 11.05 the problem returned.

When I checked the live site after the latest upgrade, everything looked fine. I suspect now that I checked during the hour that things are displaying correctly - not the alternate hours.

mudrd8mz - does this make any sense?

Warning: getimagesize(/opt/data/2/filedir/0b/07/0b07e294cbbfb166394d99cd2ce52df2832b584c): failed to open stream: No such file or directory in /opt/app/lib/filestorage/file_system.php on line 417

Warning: getimagesize(/opt/data/2/filedir/cd/8b/cd8b8112f357d14b58fa257b842b2302fb8c0a2d): failed to open stream: No such file or directory in /opt/app/lib/filestorage/file_system.php on line 417