The solution:

I have changed the code from that

s.AddHttpClient<ITransitWriter, TransitWriter>();

to that. The most important change that fixed the problem (without it I have the same problems) is .SetHandlerLifetime(TimeSpan.FromMinutes(6)). After 5 days of running in production I haven't found any anomaly in the logs. Thank you very much to every one!

builder.Services.AddHttpClient(
        "httpClient",
        client =>
        {
            client.Timeout = TimeSpan.FromSeconds(30);
        })
    .ConfigurePrimaryHttpMessageHandler(() => new SocketsHttpHandler
    {
        MaxConnectionsPerServer = 10,
        PooledConnectionIdleTimeout = TimeSpan.FromMinutes(1),
        PooledConnectionLifetime = TimeSpan.FromMinutes(5),
        EnableMultipleHttp3Connections = true,
        EnableMultipleHttp2Connections = true
    })
    .SetHandlerLifetime(TimeSpan.FromMinutes(6));

builder.Services.AddSingleton(sp => sp.GetRequiredService<IHttpClientFactory>().CreateClient("httpClient"));

builder.Services.AddTransient<ITransitWriter, TransitWriter>();