There is no filter, old wallet version can connect to the new one

many peers 3.0x are still connected, even if you restart the wallet.
No way to prevent this before hardfork. Will add that soon in next release.
Note that digiexplorer is simply a visual overlay that's not 100% accurate at the moment. Look at your core wallet "digibyted getinfo" for true network stats right now.
We are working on updating digiexplorer. All is looking good! Cheers!