@Stefano , thank you.
That way we won't need a second run at the Ubports installation.

Hello,

I've just experienced the same problem yesterday when trying to install for the first time Ubports.

On my Nexus5 the same thing: phone on the Ubports Recovery and the Installer doing nothing (wainting for the phone to get to recovery). I tried in different platforms, OS and cables and it was always the same.

It seems that the Ubports recovery doesn't behave as it should (not telling to the installer that it is available).

My solution:
1 - Launch the Ubports installer, and follow all steps until it gets stuck on the "waiting for recovery"
2 - Let the installer hanging there, but on the phone return to bootloader (you can choose the option on the phone menu, or use the key combination)
3 - install the latest TWRP via fastboot. Command like this: fastboot flash recovery twrp-X.X.X-Y-hammerhead.img
replacing X and Y for the actual version available at https://twrp.me/lg/lgnexus5.html
4 - Once twrp is installed, choose the menu option to reboot to recovery (look for it with the volume buttons and then power to select)
5 - as soon as TWRP is up, the installer will "unstuck" itself (seems twrp sends the expected commands)
6 - Let the installer go on, wait until it's finished (when it says it's safe to disconnect your phone), close the installer
7 - Open up a new installer, and begin the process again (just don't wipe data), basically we want the installer to put Ubports on the place of TWRP and the rest the phone should be able to solve by itself (with all files push in to it on the first run with TWRP)
8 - Once the Ubports recovery is installed, the installer will again say that thing about waiting for recovery, but if you look at the phone it should say something like "installing updates".
9 - Wait for the installation to complete, and wait a little bit more once the Google splash screen comes up
10 - Ubports should be up and running