There's quite a lot going on in baggage today.

Not BA related, but affecting LHR: the T1/T2 west hall sorter suffered an outage (as a reminder, T2 still doesn't have its own baggage system, using instead the T1 one). The tunnel between T5C and the main terminals also had an outage that was then fixed, and T3 integrated baggage had an issue whereby one of the movements crane crashed.

The biggest problem is that there is an issue with SITA, and that's what I think the OP message is referring to. SITA handles a lot of the baggage messaging, and there has been a loss of precisely that function. Basically, every time a bag is scanned, moved, or interacted with a baggage message is generated. This is how airlines track bags, and also how they pass info on bags from one airline to the other. Lately there have been some issues, and yesterday/early this morning there was a full outage.