@circ @domubpkm Hey so I'm having the same error code with my Ubuntu Phone VPN connexion.
I changed username and password to avoid non alphanumeric characters.
Do the name and location of .ctr and .key files have any sort of importance?

ca.crt has the form:
-----BEGIN CERTIFICATE-----
...
...
-----END CERTIFICATE-----
and ta.key has the form
-----BEGIN OpenVPN Static key V1-----
...
...
-----END OpenVPN Static key V1-----
Both are extracted from the xxx.protonvpn.com.udp.ovpn file downloaded on my protonVPN account.

Could the gateway port number be an issue?

Do you have any idea why it still doesn't work?
Thanks a lot for any kind of help or suggestion!

Edit1: Note that the password is always missing when I open the VPN editor app, but that could also just be some kind of security. Is that the expected behavior?

@advocatux Wow thanks, I didn't find this web page when I looked for this particular issue.
I already tried to open the case and blow dry air in it but i will follow those instructions this evening when I'm back home and let you know if it worked.

@Ingo Thank you for the ideas. This happens at random when the phone is switched on with screen off and I switch on the screen. Then, the colored noise can persist even after reboot.
Because of this pattern, I didn't identify any app as the troublemaker.
Thank you for the fairphone community map.

Since following 'https://support.fairphone.com/hc/en-us/articles/115001041206-Troubleshoot-your-Fairphone-2-issue > Display > My display shows a pixel image (coloured noise)' leads to the exact picture of my screen, I suppose this is most probably a known hardware issue.
I followed the instructions on @advocatux link, which means opening and cleaning every inner parts of the phone.
It works again but it has already been doing working - colored noise - working loops so I will keep you informed.