as far as I know the chained composite command is in a hidden group and thus set automatically.
for EVPN over MPLS there are no major command changes and additions
the only nice thing is the posibility to have individual addresses on the irb with a common VIP-gateway address, which means that you can sucessfully ping from the irb to the CE, however currently there is no "accept-data" feature implemented, that means you can ping from the CE the individual irb addresses but not the common gateway address
However I have no information regarding the EX9200,
Else the problem could also lie in an shared all-active ESI between the MXs and different behaviour there ? But thsi is a wild guess, as there is no information about that in your config snippets.
with best regards
Alexander