Help with Domain Name

Dear all,

somewhat unusual setup:

As I cannot access my vaultwarden server from work (“bitwarden.domain.tld”), I created a reverse proxy somewhere else as an alternate access point (bitwarden2.domain.tld).

Since all other users access the server via “bitwarden.domain.tld”, the DOMAIN variable also points to https://bitwarden.domain.tld.

Now for the interesting bit:
If I access the server via “bitwarden2.domain.tld”, then whenever I edit an entry, my session will be immediately terminated.
Using the same browser on the same device at “bitwarden.domain.tld”, I can edit the entry just fine.

Is this a bug or a feature?