The seed is AES256 encrypted as coinomi said
Since Coinomi is closed source, shady and has a history of doing very insecure things such as sending your seed phrase to a remote server, we can not know what actually happened or whether your seed is correctly encrypted with AES256. Their implementation could be flawed which could allow decrypting the file easily by exploiting it. Or maybe they are sending your seed out to a remote server again that was stolen on its way out!
Given the number of users we have we would expect thousands of users to come forward with the same issue after this update if that was the case. We are more than happy to respond to any official request to review our source code by reputable companies. We are also reviewing our decision to be closed source with the preffered outcome to be open source again.