vrrp can work across different platforms and Junos versions.
since both are active they likely are not seeing the layer 2 packets between each other.
Confirm the physical layer 2
Confirm that any protect re filter applied to the routers allow vrrp packets
If more information is needed enable trace options to get detailed logs
set protocols vrrp traceoptions file vrrp
set protocols vrrp traceoptions flag all
We actually faced same issue some times back where we had active/active.
turns out VRRP packets were not allowed via our RE-filter like spluka mentioned above.