After updating from version 4.8.18+1 to 4.8.19+4, there is an issue with being able to login to Wowza. Our development team is working on a resolution for the issue.
In the meantime, here is the workaround:
The workaround at this point if you want to continue using cleartext is to change the AuthenticationMethod to Basic in Server.xml file.
This file is located under conf/ directly such as:
Note : After editing, a restart of the Wowza Streaming Engine software is required for the change to take effect and then you should be able to login via Wowza Streaming Engine Manager.