The changelog for 2.7.0 says "Fixed an issue where OpenVPN would cause a kernel panic upon establishing tunnel." However, I'm experiencing this specific issue even with 2.7.0 installed on my Nano. I've tried several different VPN services that works perfectly fine with more beefy distros using CLI, so I'm 100% sure that the setup is working. I can follow the "negotiations" on screen when the VPN is established on the Nano, but in the end when the interface is to be brought up, the Nano resets/reboots. This happens all the time. I'm not using the available GUI module for this, but pure CLI config and execution.
Edit:
The "crashes" I experience can not be reproduced using the same OpenVPN setup on a GL-AR150 (same mips_24kc architecture as the Nano, but running OpenWrt 19.07.4, r11208-ce6496d796, kernel 4.14.195), so I guess it is either kernel related and/or has something to do with the implementation on the WiFi Pineapple Nano hardware specifically.
Edit II:
Works on the LAN Turtle and the Packet Squirrel as well (mips_24kc/19.07/4.14.134). Definitely a fruit problem since the animals are working...