Asterisk 19 to 20 Upgrade Notes
 You might be impacted by the upgrade to Asterisk 20 if you have: 
- custom Asterisk configuration
- custom application using AMI or ARI
- custom Asterisk modules (e.g.
codec_g729a.so)
If you find yourself in one of these cases, you should make sure that your customizations still work with Asterisk 20.
In particular, if you are using custom Asterisk modules, you'll need to either obtain the Asterisk 20 version of these modules or recompile them against Asterisk 20. Not doing so usually leads to major instability issues in Asterisk.
You can see the complete list of changes from the Asterisk website: