We are experiencing a bug with FileMaker Pro 18.104.22.168 running on an iMac (OS X 10.11.6). This client machine is connecting over a LAN to FileMaker Server 22.214.171.1242 running on Windows Server 2012 R2.
Please see attached screenshot.
Whenever a user scrolls a list layout (which is comprised of a header, a body part, 2 leading subsummary parts, and 1 trailing subsummary part), FileMaker is displaying grey horizontal boxes going across the entire screen where leading subsummary information would normally appear.
This user has an external display connected to his iMac, and this is happening on both his internal display and his external display. (His internal iMac display is set as the primary display.)