The tgt_last_rcvd_update() may update transaction number in client slot with smaller value. That may cause client to see wrong error message:

LustreError: 3662:0:(import.c:985:ptlrpc_connect_interpret()) pfs2dat1-OST000a_UUID went back in time (transno 77492683762 was previously committed, server now claims 77492683761)! See https://bugzilla.lustre.org/show_bug.cgi?id=9646

This is possible on OST with several IO requests from one client and safe but it is better to keep transaction value in last_rcvd monotonically increased to avoid confusion on client side.