Hi @leckylao,
it is not safe to upgrade from
@openzeppelin/contracts-ethereum-package(a similar previous package) to@openzeppelin/contracts-upgradeable.
_From: https://github.com/OpenZeppelin/openzeppelin-contracts-upgradeable/blob/master/README.md_
Also see: https://github.com/OpenZeppelin/openzeppelin-contracts-upgradeable/issues/109#issuecomment-783556754
You could use the workaround for the missing storage gap in the Initializable contract: Upgrade to contracts-upgradeable 3.3 + with EIP712 - #3 by frangio
You would then need appropriate high level tests to check for upgrade safety across versions.