panic: provider mullvad not found in hardcoded servers map; did you add the provider key in the embedded servers.json?

[gauntface]

I've been using gluetun for a while but after a recent update, I started getting this error:

panic: provider mullvad not found in hardcoded servers map; did you add the provider key in the embedded servers.json?

I use the wireguard configuration similar to https://github.com/qdm12/gluetun-wiki/blob/main/setup/providers/mullvad.md

I've tried using SERVER_CITIES and/or SERVER_COUNTRIES and tried with a different wireguard private key and address (following steps on #805 (reply in thread))

Has anyone encountered this / have any recommendations for fixing this issue?

[gauntface]

I ended up using qmcgaw/gluetun:v3.39 for the image and it worked as expected, suggesting a change in v3.40 is causing the issue.