strange problem when rendering

Hi, we ran into a rather odd problem, yesterday, and I hope you can help me with this:

We are compositing some cgi elements into Alexa footage and everything looks fine when viewed from within Fusion (version 18.1.1 that is), ie. when we view the final saver (in our case lifesaver) node in any one of fusion's viewers, everything looks as expected.

When rendering the saver, however, the frame immediately displays slightly blurry with a noticably blurred, transparent fringe, and it writes files that do not show whatever we previewed before: Some tracker removal seems to be absent from the files written entirely etc.
When we abort the render the content displayed in the viewers is now also that blurry, incomplete version. Now, whenever we change anything within the script - say toggle motion blur on and off on a node or similar - the display switches back to the correct/expected content being displayed.

Finally, when we play within the GUI and force fusion to cache frames, we can then save out what has been cached, correctly.

Any idea what could be causing this and how to fix this? It seems like not the entire script is computed when rendering... Any help is greatly appreciated, as our dirty workaround - for the time being - is to hit play within fusion, cache everything as far as possible and then write out the cached frames. Piecemeal style... urgs

Sounds like a node somewhere in there might be corrupt. Sometimes you can fix this kind of thing by copying the nodes to a fresh composite—just select all, copy and paste. That will cause Fusion to actually generate new nodes, potentially discarding any corrupt data.

If that doesn't work, my next troubleshooting step is to try to isolate the portion of the comp that's causing problems using a binary search testing method. Connect the Saver to a node half-way between the start and end, and see if the problem happens. Then move it forward or backward, depending on the results, until you've narrowed it down to a small area. Then you can start disabling things in that vicinity to try to find the culprit.

Be aware that occasionally the problem can be caused by a combination of two or more nodes and not just one. How exactly to resolve it from there depends on what's going wrong and whether it's easier to try to actually fix it, bypass it, build around it, or what.

A few more general tips that can sometimes fix weird issues: If there are Transforms of any kind involved, try ticking the Flatten Transform checkbox; this will break concatenation, so don't go crazy and check it on everything, though. If there are mask nodes that are getting their resolutions implicitly, set them manually to the desired resolution. Change Fast Gaussian to Gaussian on anything with a Filter parameter. Disable GPU Processing.

I'm pretty sure there are a few other generic things of that sort you can try, but those are the ones that were at the top of my brain.

Thank you so much, Bryan! ..... -> !!
Not only for the great tips in general, but specifically for pointing me to the transform node because that, indeed, fixed our issues! If you are ever in Vienna: I owe you a beer or two!

I noticed that Planar tracker in combination with Matte Control is better not to use. And it doesn't matter where in the script it is. I avoid using a combination of these tools together. Although individually they work well.

I thought of one more thing: In the Saver, you can set the Save Frames control to Hi Quality Interactive (just Interactive for LifeSaver). Instead of using the Render process, it saves them the frames to disk when you view the Saver node in the viewport. When all else fails, if you can see the desired image in the viewer, this mode will let you save it.

It's a last resort, employed when I'm at my desk at 11pm, in tears because I'm so tired, and there's a drop-dead delivery in the morning.

Gosh, now I remember why I'm not in production any more!

Do you know a script to turn off GPU for a render? So if you send a comp to a network render it would disable the GPU usage?

To do it when sending a network render, you'd probably want to put it in a submitter script, but I have a pair of comp scripts to manage GPU features. See the attachment. Feel free to adapt as desired