I one SEPM have problem because can't run luall.exe from schedule. When run manull all is OK.
In Log.LiveUpdate I see entry
HttpSendRequest (status 502): Request failed - Gateway or proxy encountered an error on the LiveUpdate server.
Could Give same advice
SEPM is in 12.1.ru2 LU in version 3.3
This option I do
lucatalog -cleanup and press Enter.
then lucatalog -forcedupdate