Just adding to what @Osiris said:
First, you can verify your server is sending the right chain using a site like this one:
https://decoder.link/sslchecker/gallery.vote/443
I found these Twisted docs:
https://twistedmatrix.com/documents/21.2.0/api/twisted.internet.ssl.CertificateOptions.html
Their docs in general are not very helpful but you might try using the chain.pem file from Certbot as your extraCertChain value when setting up the server ssl options.
If that does not work getting help directly from Twisted or its community is best.