Messages Getting Stuck at "Holding"

Hi,

Just recently (i.e. since our SAP year end) occasional messages for a particular scenario are getting stuck at a status of "Holding". Below is an example of one:

Another occurrence of the same message type later in the day does not get stuck i.e.:

There are no errors and no queues in SMQ2.

Can anyone out their advise why messages may from time get stuck at "Holding" ?

Cheers,

PaulC.