Upgrade to v28.0.0.2 (from 27.0.0.0): Must upgrade to v25 first!

Please advise how to fix this. Thanks.

Upgrading from a version earlier than 25 requires upgrading to version 25 first (from any earlier version directly). And then from version 25 directly to the latest version.
Such a message is not expected to show up when using a version higher than 25, unless something is mixed there, like an old version merged with a newer one. We'll be happy to start by reviewing your log files. Please reach out to support@ and we'll continue from there. Thanks.