You are quite right; it took me a while to find it, but a v5 F@H was lurking.
It is now removed and I have both machines running now.
This is how things are currently:-
[16:52:57] Completed 2500000 out of 2500000 steps (100%)
[16:52:57] Writing final coordinates.
[16:52:57] Past main M.D. loop
[16:53:57]
[16:53:57] Finished Work Unit:
[16:53:57] - Reading up to 153648 from "work/wudata_02.arc": Read 153648
[16:53:57] - Reading up to 1242248 from "work/wudata_02.xtc": Read 1242248
[16:53:57] goefile size: 0
[16:53:57] Leaving Run
[16:53:57] - Writing 1439324 bytes of core data to disk...
[16:53:57] Done: 1438812 -> 1365552 (compressed to 94.9 percent)
[16:53:57] ... Done.
[16:53:57] - Shutting down core
[16:53:57]
[16:53:57] Folding@home Core Shutdown: FINISHED_UNIT
[16:54:01] CoreStatus = 64 (100)
[16:54:01] Sending work to server
[16:54:01] Project: 6331 (Run 6, Clone 478, Gen 12)
[16:54:01] - Read packet limit of 540015616... Set to 524286976.
[16:54:01] + Attempting to send results [July 30 16:54:01 UTC]
[16:54:02] - Couldn't send HTTP request to server
[16:54:02] + Could not connect to Work Server (results)
[16:54:02] (171.64.65.60:8080)
[16:54:02] + Retrying using alternative port
[16:54:03] - Couldn't send HTTP request to server
[16:54:03] + Could not connect to Work Server (results)
[16:54:03] (171.64.65.60:80)
[16:54:03] - Error: Could not transmit unit 02 (completed July 30) to work server.
[16:54:03] Keeping unit 02 in queue.
[16:54:03] Project: 6331 (Run 6, Clone 478, Gen 12)
[16:54:03] - Read packet limit of 540015616... Set to 524286976.
[16:54:03] + Attempting to send results [July 30 16:54:03 UTC]
[16:54:04] - Couldn't send HTTP request to server
[16:54:04] + Could not connect to Work Server (results)
[16:54:04] (171.64.65.60:8080)
[16:54:04] + Retrying using alternative port
[16:54:05] - Couldn't send HTTP request to server
[16:54:05] + Could not connect to Work Server (results)
[16:54:05] (171.64.65.60:80)
[16:54:05] - Error: Could not transmit unit 02 (completed July 30) to work server.
[16:54:05] - Read packet limit of 540015616... Set to 524286976.
-------------------------------------------------
[17:16:44] + Attempting to get work packet
[17:16:44] - Connecting to assignment server
[17:16:45] - Couldn't send HTTP request to server
[17:16:45] + Could not connect to Assignment Server
[17:16:46] - Couldn't send HTTP request to server
[17:16:46] + Could not connect to Assignment Server 2
[17:16:46] + Couldn't get work instructions.
[17:16:46] - Attempt #9 to get work failed, and no other work to do.
Waiting before retry.
And the latest (Saturday lunchtime):-
[10:24:01] + Attempting to get work packet
[10:24:01] - Connecting to assignment server
[10:24:02] - Couldn't send HTTP request to server
[10:24:02] + Could not connect to Assignment Server
[10:24:03] - Couldn't send HTTP request to server
[10:24:03] + Could not connect to Assignment Server 2
[10:24:03] + Couldn't get work instructions.
[10:24:03] - Attempt #31 to get work failed, and no other work to do.
Waiting before retry.
XB