the upgrade documentation here https://access.redhat.com/documentation/en-us/red_hat_3scale_api_management/2.2/html-single/infrastructure/index#gather is incomplete.
in particular it states that 2.2 needs 4 new variables which according to the instructions have default values: You may choose to either specify new values for these parameters or keep the default ones.
This is not true for master access token (MASTER_ACCESS_TOKEN) which might be automatically generated during the upgrade but it is not added to the system seed by default

This can cause issues also in the upgrade from 2.6 to 2.7, given the critical usage of MASTER_ACCESS_TOKEN