Make sure that you haven't banned the bitnodes crawlers by accident.
Remove them from your banlist using these commands:
bitcoin-cli setban 88.99.167.175/32 remove
bitcoin-cli setban 88.99.167.186/32 remove
bitcoin-cli setban 2a01:4f8:10a:37ee::2/128 remove
You might also find this thread helpful:
My node is not reachable from Bitnodes, other wallets: maxed out incoming peers?