Hi, Cloud.
I recently came across a similiar issue after upgrading from 15.x code to 17.2R2.8. I confirmed the ARP table had no entry for the RLT interfaces and the output of show interface rlt0.0/rlt0.1 lacked a MAC adddress. Checking another device that ran 15.x the ARP entry and MAC were both programmed properly.
To get around this you can install temporary destination MACs. Warning, this should be done on point-to-point RLTs.
set interfaces rlt0 unit 0 family inet address 192.168.10.210/31 arp 192.168.10.211 mac e8:b6:c2:b2:3b:42 set interfaces rlt0 unit 0 family inet address 192.168.10.210/31 arp 192.168.10.211 publish set interfaces rlt0 unit 1 family inet address 192.168.10.211/31 arp 192.168.10.210 mac e8:b6:c2:b2:3b:43 set interfaces rlt0 unit 1 family inet address 192.168.10.211/31 arp 192.168.10.210 publish
Committing gave us a successful workaround. I have requested further review from Juniper and if a PR is generated I will update the post with the info. I hope this helps!