Hi loba-ucb,
Please be advised that EX4650 can't be stacked with other platforms, as you can see below,
https://www.juniper.net/documentation/en_US/junos/topics/concept/virtual-chassis-ex4200-overview.html#jd0e747
"EX4650 switches can’t be combined with any other type of switches in a Virtual Chassis."
You can only stack up to 4 EX4650 after 20.1R1 code.
"Starting in Junos OS Release 19.3R1, you can interconnect up to two EX4650 switches in an EX4650 Virtual Chassis. The two member switches must be in the master and backup Routing Engine roles.
Starting in Junos OS Release 20.1R1, you can interconnect up to four EX4650 switches in an EX4650 Virtual Chassis. You should configure two member switches into the master and backup Routing Engine roles, and the remaining member switches into the linecard role."
If this worked for you please mark as "Solved" so we can help others too.
Regards,
Jeff