Hi J,
Greetings of the Day!!!
Please ensure you have same version of JUNOS on all members of virtual chassis cluster-
>show version
Check whether & if the troubling member is booting with primary partition and check the version on it-
>show system storage partitions
>show system snapshot media internal
Also please use the following command strictly if there are only 2 members in virtual chassis-
#set virtual-chassis no-split-detection