Thanks for the help - resetting to default settings helped. Again I can see a preview of the effects. Although I still do not know why sometimes it blocks. Anyway - great thanks!

NVidia GPU and driverversion?

GeForce GT 740M, driver version: 384.94

Are you using a Nvidia gpu?

Yes, in version as I said bellow.

Cornico may well have a point.

Hi everyone

Same issue here, so I wrote to tech support and after more than 2 weeks I got this answer

Hello

Thank you for your message.

​Lets have you install the application to the hidden administrator profile for troubleshooting purposes. 

"Windows comes with a hidden administrator account which must first be enabled.  To do so:
1. Type  "Command Prompt" into Windows search or Cortana 
 2. right-click on the Command Prompt result that appears and choose  "Run as administrator" 
3. After the command prompt opens, type:   net user administrator /active:yes
4. Double check to make sure the command is entered correctly and hit Enter on your keyboard.
5. After running this command, the prompt will respond with:  command completed successfully
6. Switch to the administrator account by clicking control+alt+delete, then click switch user, and choose Administrator.
7. Install and activate your VEGAS application onto this profile"

It does works but I have to switch profile in order to make it work and that's not really convenient 'cause I cannot access my document so I have to work with an USB key :-(

What about just right clicking on the .exe file and clicking 'run as administrator'. Does that help?

I've seen the same behavior when I set the GPU to Nvidia. I haven't gone to the trouble of downgrading the driver because I've found that if I set the GPU to my other chipset, Intel, that the previews work fine when editing titles or fx

It might be possible to affect these results in another way. I haven't had the opportunity to try this yet.

If you have both nvidia and other (likely intel) chips on your system, the nvidia driver will let you choose which is the primary gpu. I currently have mine set to Nvidia.

Before I settle on an answer, I'd want to benchmark operations to see which one gives me the best rendering results and speed.

Actually, I might not need to do the latter test. I remembered I did some rendering tests when choosing my new laptop in May and using the Nvidia GPU resulted in renders taking half the time vs the Intel chipset or nothing at all.

I might have to try downgrading the driver after all.

Ok, I did have a moment to try one experiment.

If you have two GPUs and one is Nvidia, tell the Nvidia driver to auto-select your GPU and choose the Nvidia GPU in Movie Studio. Previews will update properly when editing titles and fx.

You'll likely get decreased performance by default in other apps that don't let you explicitly choose the GPU but your editing in MS will work properly (and rendering will be faster).

You can set per-app profiles in the Nvidia driver which should allow you to work around this last limitation.

@michael-harrison does the NVidia app over-rule the Bios setting (or change it)?