Yep. Classic issue with many plugins.
I’ve developed a workaround to basically never see this issue again and it involves:
Render the “Whole Montage” as a continuos file. You can tell WaveLab to Copy Markers and create new montage from resulting file when you do the render of the Whole Montage.
Then you end up with a new montage with all your plugin effects printed (and no glitches), and most of your original project data and decent starting point again. You may need to repopulate CD-Text info depending on your workflow.
Now you can render continuous WAV files of each audio track and when you line them back up in a DAW or media player to test, you will have seamless playback as you want. You don’t even have to worry about zero crossings. I worry more about marker quantization so that my DDP masters perfectly match the WAV masters than I worry about zero crossing and track IDs.
You can decide to dither on the “Whole Montage” render, or wait to dither until you render the individual tracks. I find that the MBit+ dither running on the montage output effects doesn’t cause this issue so that is safe to run on your second rendering of tracks, but definitely more intense plugins will cause issues with gapless playback if you render one track at a time. This is because as silly as it sounds, the plugins need “warm up” time and when you render a WAV of each track, it’s a lot of starting and stopping of the plugins. Best to print all effect in a continuous render of “Whole Montage”.
I personally do the initial render as 32-bit WAV and then apply dither later when I do the individual track renders so it’s easy to make 24 or 16-bit WAVs from the same “Whole Montage” render. Keeping the first render as 32-bit float prevents you from being locked in.
This is an issue that has been discussed but not yet fixed.
As a test, try this same process but with no plugins involved and I think you’ll find that the issue is not from the track splice, but rather a plugin being used and trying to render gapless/seamless audio from CD tracks.