The password specified for that option is unrelated to your master password and only used to encrypt the export file. Also you should never use your master password (or any important credentials) as a command line parameter since those are visible in the process list of the system. A much better way is to use environment variables.
I am not sure how this should have worked for your exports performed previously with the older CLI version.
Usually you use bw login (documentation). For automated workflows, a personal API key is recommended. After login or unlock, you retrieve a session key that can be used for all future commands.