my after effects preview is blank

Do you have Intel GPU's enabled on those machines? We've seen reports that some Intel drivers are causing issues when there are also NVIDIA drivers installed.
 
Here are some steps to try:
 
• Close After Effects
• Go to the Device Manager (Run >> devmgmt.msc)
• Select Display Adapter, Right click on  the "Intel UHD graphic card".
• Select "Update Driver"
• Select "Browse my Computer"
• Select "Let me Pick from a list of available drivers on my Computer".
• Select "Microsoft Display Adapter".
•  Launch After Effects.
 
Let us know.