If the number of "incoming" connections is 0, then you are NOT running a "full" node... Other nodes are not able to connect to your node and request block and transaction information etc.
To receive incoming connections you need to make sure the "allow incoming connections" option in "Settings -> Options -> Network" is checked.
Alternatively you can use the listen=1 option in bitcoin.conf (or -listen=1 command line argument when starting bitcoind)
Refer here: https://bitcoin.org/en/full-node
And, more specifically, here: https://bitcoin.org/en/full-node#network-configuration