VSTs randomly ignored on certain clips

I’m a fairly experienced hobby editor working in Resolve Studio 18.0.3, but I had this issue in 18.0.1 also.

My current project has a timeline of about 100 clips, most of them with audio requiring RX9 denoize, and also a music track.

I encountered a bug wherein certain clips would just not process the denoise VST unless I happened to be playing the clip while enabling the VST effect on it, then it would render in real-time, and then again not render on the second play through, letting the noise go through. This would happen during playback as well as on export, and in bouncing the mix to a new track (more on that in a second).

Setting “cache audio effects” would sometime force it to reliably render the denoised audio, sometimes not. Sometimes a compound clip would work, but not reliably enough.

Because VSTs don’t get processed in audio-crossfades, I had to make a bunch of J and L cuts for some clips and eventually once I had a stable mix I started trying to Bounce the whole mix to new track to bake in the denoising.

This is where things got very bad. Certain clips would just refuse to playback any audio, even though waveforms were still visible on the timeline and in the audio-waveform scroller. This happened in the bounced mix as well as the original tracks where they had previously been working fine.

Removing all effects from the affected clips wasn’t fixing the issue. I tried a dozen things, eventually I noticed moving the audio to a new track that had no dynamics processing was getting some of the clips back. Lots of reboots and cache deleting and so forth later, I eventually was able to bounce a mix but it still had lots of glitches in it: pops where I had cross fades, a bunch of missing samples in random places, and some clips with still no VST processing, etc.

Is there any workaround for this mess? I lost an afternoon just trying to salvage my edit.

Is this behaviour experienced with all plugins or is this isolated to iZotope RX plugins?

Audio Plugins incur latency and can require greater system resources depending on the processing required, especially iZotope RX plugins.

Clip effects are not latency compensated whereas Track inserts are.

Adjusting the block size via Resolve's Preferences may improve performance:
System > Video and Audio I/O > Audio I/O > Playback processing buffer size

The Fairlight “Cache Audio Effects” and the “Bounce Audio Effects” functions may sometimes remedy the issues with processor intensive plugins.

If using iZotope RX plugins, consider configuring the standalone RX Editor as an External Audio Process: Preferences > System > Audio Plugins > Setup External Audio Processes

Adjusting the block size via Resolve's Preferences may improve performance:
System > Video and Audio I/O > Audio I/O > Playback processing buffer size
If using iZotope RX plugins, consider configuring the standalone RX Editor as an External Audio Process: Preferences > System > Audio Plugins > Setup External Audio Processes

These are great suggestions, thanks so much for taking the time. I'll play around with it and see if I can't get control of my timeline's audio back.

Even if it is a realtime processing issue, it would still be a pretty massive bug that it impacts caching, bounces, and exports, but this might help me work around it and save my project.

I hadn't tried with other effects at the moment since I was pretty focused on trying to fix my current project but I will find some time to investigate further and file a proper bug report if I can.

I noticed in the recent forum posts another user was having similar buggy issues with a Waves plugin on all versions 18.0.1 through 18.0.3 but that sticking on 18.0 was giving him stability, so I have that I could try also.

Adjusting the block size via Resolve's Preferences may improve performance:
System > Video and Audio I/O > Audio I/O > Playback processing buffer size

Reporting back on results, which were mixed.
TLDR; it worked well enough to get a good clean bounce of my timeline audio, but only worked during that one session and on subsequent session it went back to previously described behaviour.

I changed the buffer from "auto" to a full 4096 samples and that seemed to help immensely. I had to uncache all previously-cached effects and manually delete my audio render cache folder, but I managed to get a much cleaner bounce and that's when I realized that it wasn't just the RX that was getting ignored a lot. Even what I thought was a clean bounce had basically ignored all volume keyframes and a bunch of crossfades, and so on.

Sadly, after switching to another project and back, I can't get it to work well again anymore. If I set windows to use another interface other than the motherboard codec, I can't even switch off of Auto buffer. And on a subsequent session, when using the mobo codec and setting buffer to 4096 samples, I was once again experiencing certain clips just ignoring the RX effect altogether during playback and bounce.

Thanks again Reynaud for your suggestion. At least I got it working long enough to print a reasonably clean soundtrack for my project. Lucky the editing was nearly done... guess I'll have to call it done!