Hi @dmdv,
Slither is reporting that the reserved storage gap __gap shadows the other gaps in inherited contracts. For information on the gap please see the following: https://docs.openzeppelin.com/contracts/3.x/upgradeable#storage_gaps
As the storage gap is only used to reserve space I don't think shadowing is an issue.
I assume you are compiling with Solidity 0.7.
In Solidity 0.7 visibility ( public / external ) is not needed for constructors anymore.
See: https://docs.soliditylang.org/en/v0.8.0/070-breaking-changes.html#functions-and-events
If you want to use Solidity 0.7, you may prefer to install
@openzeppelin/contracts@solc-0.7
For the combination of upgradeable contracts and Solidity 0.7, use@openzeppelin/contracts-upgradeable@solc-0.7
From: OpenZeppelin Contracts 3.3
You appear to have a mix of upgradeable and non-upgradeable contracts. For upgradeable contracts you should use OpenZeppelin Contracts Upgradeable, see: https://docs.openzeppelin.com/contracts/3.x/upgradeable
I would go through all of the reported issues/warnings and either resolve or decide why it doesn't need to be resolved. I would suggest documenting this for your community.
Last full audit on v2.0.0, see: https://github.com/OpenZeppelin/openzeppelin-contracts/tree/master/audit