TCP reset on 50% of http POST

[Pieter1234]

Since MacOS Big sur I get about 50% TCP reset's. This can be reproduced with curl:

$ curl  -d '{"request": "query"}' -H "Content-Type: application/json" -X POST http://local_network_host:21573/ >/dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 14668    0 14648  100    20   133k    186 --:--:-- --:--:-- --:--:--  133k
$ curl  -d '{"request": "query"}' -H "Content-Type: application/json" -X POST http://routingtestb:21573/ >/dev/null
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 14668    0 14648  100    20   133k    186 --:--:-- --:--:-- --:--:--  133k
curl: (56) Recv failure: Connection reset by peer

I'm not able to reproduce with a public host yet. I can provide a pcap but prefer not to make it public.

Tried:

• Only NAT network. Did not try bridge.
• Tried various adapter types.
• Multiple hosts have same issue.
• Different guests have the same issue. (Windows / Linux)

[Pieter1234]

Forgot to mention: On host system the curl command is working flawlessly.

[Pieter1234]

Update: I'm starting to doubt it a VirtualBox issue. I do have similar problems on host. I'll update if I change my mind (again) :)