It’s fixed:
/routing filter rule
add chain=bgp-backbone rule="append bgp-communities 65001:11111"
add chain=bgp-backbone rule="append bgp-communities 65001:22222"
add chain=bgp-backbone rule="append bgp-communities 65001:12345"
add chain=bgp-backbone rule="append bgp-communities 65001:54321"
add chain=bgp-backbone disabled=no rule="delete bgp-communities 65001:54321"
add chain=bgp-backbone disabled=no rule="if ( afi ipv4 && dst in 10.0.0.0/8 && dst-len <30 ) { accept }"
> /routing/bgp/advertisements/print detail
0 peer=peer-130 dst=10.x.y.0/24 afi=ip local-pref=100 nexthop=10.i.j.4 origin=0
communities=65001:22222,65001:12345,65001:11111
seems fixed! Looking forward to the stable release, to get it fixed in prod as well.