The theme is resetting to default for some users every 7 days. Jim_Starkweather initially thought it might be due to session expiration or client-side clearing. However, Falco identified the issue as related to Apple devices’ default behavior of removing cookies after 7 days. This causes the custom theme to reset when the cookie is removed.
To work around this, Falco suggested applying the theme to all devices, which saves the preference on the server. Other options include not visiting the site for 7 days, using a different browser on MacOS, or installing the Discourse PWA on iOS. Jim_Starkweather confirmed this explanation matches the reported behavior.
From what they are telling me they are using Discourse from that device, the theme changes, they change it back and then 7 days later on that same device they see it revert back to the default theme. I can ask them about using it on other devices, but isn’t the theme choice set in their profile settings, etc?