Unstable FPS and bitrate compared to SRS Stack

[xaderil]

Hello. I'm already feeling discouraged and don't know what to do.

I need Forward to determine the array of endpoints for restreaming for each user, but when streaming with the following config (or any other), there are FPS drops and unstable bitrate.

listen              1935;
max_connections     200;
pid                 ./objs/srs.backend.pid;
daemon              off;
srs_log_tank        console;
srs_log_level       verbose;

vhost __defaultVhost__ {
    transcode {
        enabled on;
        ffmpeg ./objs/ffmpeg/bin/ffmpeg;

        engine {
            enabled on;
            vcodec copy;
            acodec copy;

            perfile {
              re;
            }

            output output rtmp://127.0.0.1:[port]/[app]/[stream]_[engine]?vhost=[vhost];
       }
    }

    forward {
        enabled on;
        backend https://xxxxyz.com/api/forward;
    }

    http_hooks {
        enabled         on;
        on_publish      https://xxxxyz.com/api/streamstatussrs;
        on_unpublish    https://xxxxyz.com/api/streamstatussrs;
    }
}

Streaming is done through OBS and the settings should be copied. No extra transcoding should occur.

But all the options I've tried don't give any result, streaming is almost impossible due to the drops.

At the same time, out of curiosity, I launched SRS Stack, specified the restream address, and with the same OBS settings (zerolatency, veryfast) I got a perfectly stable FPS without any drops and a perfectly stable bitrate. After digging into the SRS Stack code, I found that for forward it simply runs ffmpeg with a configuration similar to transcode in the config above. Now the question is: why does SRS Stack give a perfect restream result, while SRS makes restreaming impossible?
There are no errors or warnings in the logs.
I'm asking for your help in solving this mystery.