Resolve 18 rendering issues

Just updated from Resolve Studio 17 to 18 and I'm now having rendering issues. A couple small projects rendered out fine, in just a few minutes. Then another, almost identical, took over an hour (crashed the first time). A similar project in a different timeline (but setup very similarly, and which I've rendered from in the past just fine) is telling me the render time will take almost 13 hours (that's down from the days it initially calculated).

I double checked my hardware preferences in Resolve and everything looks okay.

My system:

Win 11 pro. Ryzen 5 5600X. AMD RX 580 (8 GB dedicated memory). 16 GB system RAM.

During this particularly messed up render my CPU usage is at 12%, my GPU usage is at 0 to 1%, and my RAM is at about 40% usage. In the normal renders I did previously, GPU usage was around 60-70%, and CPU was maybe around 20-30%.

Oh, and this project plays back fine in the timeline, and is only about 2 minutes long (at quarter resolution, including all color and fusion effects turned on). If I stop the rendering it half-way locks up Resolve. I can't switch out of the delivery tab, or do most things, but I can move the play-head around.

UPDATE:

Well, after Resolve crashed I restarted Windows. Now the project loads very slowly, crashed Resolve once, after that I could get in but it's not responsive at all, won't play, etc.

I ended up just rebuilding my fusion clip from scratch and it seems to have fixed the issue (who knows why??). That's for the particularly bad rendering issue I was having. I have many more such projects to render, so I'll report back if I notice any patterns.

Okay, after a lot of frustration I think I've found a pattern with some of these rendering bugs in 18. They relate to Fusion.

For some of these little projects I have one single PNG file in Fusion that is being moved around via a transform node. Those projects render out just fine, as they did in v.17. For the projects that already had a Fusion clip (created in v.17), those say they will take over a day to render out (something that in 17 took about 3 minutes). So for me I've found that I have to build Fusion clips from scratch in v.18, even though I'm building them exactly as they were in 17. Luckily I don't have many of these to do.

The second bug is potentially worse:

Some of my little projects include two PNG files in a single Fusion clip, both being moved around via a transform node exactly as described above. It doesn't matter if I create these Fusion clips from scratch in v.18, they will still take many times longer to render than the versions with a single PNG file in Fusion. For a 1 minute video, that means nearly an hour to render a video that in v.17 would have taken around 6-8 minutes. While Resolve is rendering these, CPU usage is about 5%-7%, and GPU is about 50%-60%. Plenty of free RAM.

Are you using a MediaIn or a Loader node for the pngs?

MediaIn (dragging the PNG in makes this by default I think). But I can try a loader node...

Ah, using loader nodes seems to work perfectly. Thanks so much!

hello! I meet this issue pretty often in DR 18.5

Very often I work with files from Panasonic GH6 H264 422 log-V UHD
and from time to time I face the same problem: one or two files going to pixelate after rendering.
Other files are ok

I use CST from log-V to r709 and some adjustments with contrast and color... nothing extreme

Who knows what is going on with files?

These screenshots are from the same file at the beginning and the end of it.