Hello,
I am no expert on Huawei, but what You described looks like reth3 MAC did not get re-learned by Huawei #1 after RG2 failover.
In more detail:
1/ SRX RETH has single MAC, much like LAG
2/ this MAC is seen only on active RETH member(s)
3/ when RETH fails over, RETH sends gARP and his MAC starts to be seen on new active member(s)
4/ this gARP is supposed to rewrite MAC table entry on all L2 devices it travels through and to
5/ it looks like this gARP is either not reaching Huawei #1 through Huawei #2, or Huawei #1 does not react on this gARP.
HTH
Thx
Alex