Another important observation. VPN tunnel through Archer C2300 works without issue when using 2.4 GHz. So it is failing only with 5GHz WiFi. I wish somebody would tell me this before I spent hours on...

@miro_miro I just found out this similar issue (or even same) was reported here: https://community.tp-link.com/en/home/forum/topic/168374 without any reasonable solution to it.

My router Archer C2300 restarts itself when starting VPN connection tunnel through it. My settings: NBN --- Archer VR1600v --- lan cable --- Archer C2300 (AP mode) --- wifi --- PC The only thing chat...

This is starting to be ridiculous. My router restarts itself when I just want to use VPN tunnel through it. Your page https://www.tp-link.com/au/support/contact-technical-support/#E-mail-Support says...