VST3 Nuendo/Cubase specific Export processBlock Time

Hi all,

I’m making VST3 Plug-In target for Reaper, Cubase, and Nuendo.
When I export track audio files in DAW, I write a wave file using processBlock to record and merge original sound data.
In Cubase and Nuendo, the sound length was different from exported files and my written file.
Diff time is about 1.3 seconds. It seems to be related to sample rate and block size.
But Reaper doesn’t happen it.

Nuendo and Cubase seem to give special time to processBlock.
But I can’t find the specific time.

I want to know specific time, please let me know if you know something about it.