Could a network connection problem between MetaMask and Ganache trigger "internal JSON-RPC errors"? How can I check this?

Yes, if MetaMask cannot reliably communicate with Ganache, it can lead to JSON-RPC errors. Verify that Ganache is running and accessible on the configured network address and port. Check your firewall settings to ensure that MetaMask can connect to Ganache's server. Try restarting both applications to refresh the connection.