PacketTunnelProvider - Issue with inbound TCP traffic

Hi,

MacOS Version- 10.15.6

I have a remote access VPN application which made use of KEXT earlier and now I have migrated to NetworkExtension framework. I am running PacketTunnelProvider as SystemExtension.
I maintain two threads, one for reading packets from utun and other for writing packets to utun.
Here is a gist of my packet handler threads.

1. Reading packets from utun

Code Block 
read_packets_from_utun(){
   [tun_device.packetFlow readPacketsWithCompletionHandler:^(NSArray<NSData *> * _Nonnull packets, NSArray<NSNumber *> * _Nonnull protocols) {
    send_packets(packets, protocols);
     
  }];
}
send_packets(packets_array){
        pcount = packets_array.count;
        for(int i=0; i<pcount; i++){
            // Encrypt and send packet to server
            encrypt_and_send(packets_array[i]);
        }
		// Read next packets
}

The 'send_packets' function then encrypts each packet in a loop, sends it to the server and then calls 'readPacketsWithCompletionHandler' again in order to keep receiving packets.

2. Writing packets to utun

Code Block 
NSArray<NSData*>* packet_array = [NSArray arrayWithObject:packet];
    NSArray<NSNumber*>* proto_arr = [NSArray arrayWithObject:proto_num];
    [tun_device.packetFlow writePackets:packet_array withProtocols:proto_arr ];

After decrypting each packet, I write each packet back to utun via writePackets call.

Question. Is this the correct way of using writePackets call?

I ran some performance tests using iperf with the system extension and observed the following. (I also compared the performance numbers with that of older application with KEXT).

1. Performance for UDP traffic (bidirectional) is observed to be the same for both the SystemExtension and KEXT.

2. Performance for outbound TCP traffic (Macbook sending data to remote server) is found to be the same for both SystemExtension as well as KEXT.

3. There is performance degradation seen for inbound TCP traffic (remote server sending data to macbook).

The performance is degraded to approximately 10% of that of older app(KEXT).
I also tried buffering packets before writing to utun, but there was no luck :(

Am I missing something while handling packets?

If that's not the case, Is there any known issue with TCP traffic with PacketTunnelProvider?

Thanks.