I’ve just had this issue when updating a Discourse install…
I believe the cause is because when DISCOURSE_MAXMIND_LICENSE_KEY is specified in the .yml container file without a corresponding DISCOURSE_MAXMIND_ACCOUNT_ID.
@tgxworld’s pull request adds the use of DISCOURSE_MAXMIND_ACCOUNT_ID in multiple places and explains the need for “Account ID”:
For me the fix was adding DISCOURSE_MAXMIND_ACCOUNT_ID and rebuilding (I rebuilt twice, but this was most likely a temporary issue).