Hi,
The proportion guides in V-Ray camera don’t show up. Screenshot below.
They tend to be a bit wonky, they disappear for me sometimes but 99% of the time they show. I can force them to show by enabling/disabling them clicking on another object besides the camera or showing safe frames.
There’s a known issue (internal tracker id: VMAX-14218 ) with Proportion guides, which occurs when the Near Clipping plane goes beyond the Target Distance. However, based on the screenshot, this doesn’t seem to be the case on your end. Do the guides appear if you disable camera clipping? Maybe you could delete everything except the camera from the scene and attach it here - I presume the issue will still be there.
I found the cause of the problem! I had the cameras hidden in the “Hide by Category” menu in the Command Panel. Unhiding them revealed the guides.
Here are other cases that I found make the guides disappear:
- Hiding the camera target.
- Setting the camera near clipping plane to over 600cm. It’s important to note that even disabling the clipping doesn’t fix this. You need to have the near clipping plane to less than ~600cm in either cases, no matter if camera clipping is turned on or off.
- Using per-viewport filters and setting them to “Show Renderable Only” or using “Show by Category” where the cameras are turned off.
Basically, anything that hides the cameras in the viewport seems to hide the Proportion guides too. I hope this helps other people that encounter this problem. 
Ah that explains a couple of things. Although I rarely use camera target, or do you mean just hiding the target if it’s enabled.
Yes, if you use a targeted camera, if you hide its target, the proportional guides will hide as well.