Windows OS
Close out FileMaker Pro (if application is still running)
Open File Explorer
Navigate to %localappdata%\Temp
Select and Delete subfolders "ContainerCache, DBCache, DBFielThumbnails, QuickStart"
Relaunch FileMaker Pro
MAC OS
Close out FileMaker Pro (If application is still running)
Open "Finder"
Navigate to "Go" > "Go to Folder" > "~/Library/Caches" Folder
Select and Delete "com.filemaker.client.advance12" or "com.filemaker.client.pro12"
Find the 2nd FileMaker Folder > Delete all contents within that 2nd FileMaker Folder
Restart the computer
Relaunch FileMaker Pro