There is a problem with your configuration, not letsencrypt : https://www.ssllabs.com/ssltest/analyze.html?d=montbot.com&latest the chain issue means you don’t provide the correct list of intermediates certificates
There is a problem with your configuration, not letsencrypt : https://www.ssllabs.com/ssltest/analyze.html?d=montbot.com&latest the chain issue means you don’t provide the correct list of intermediates certificates