I get this error, when I try sending a test e-mail from the status page, and some subscribers does not get any newsletter;
Last test failed with error “Undefined index: name”.
I also have these errors;
You have the PHP opcache active with file validation disable so every blog plugins update needs a webserver restart!
The recommended charset for your database is utf8mb4 to avoid possible saving errors when you use emoji. Read the WordPress Codex conversion instructions (skilled technicia required).
About the undefined index, is reported even the line of code? About opcache, someone configured it in an aggressive mode, the provider can change that setting. Again, the latin1 database is a very old encoding, ask the provider to migrate it to utf8mb4 enconding.