Generally speaking this is a very broad question. However, I’ll try to answer on a high-level.

First thing to consider is that the Prosys OPC UA Java SDK is not designed to be deterministic in its execution. It’s expected that program execution cannot be guaranteed when using non-realtime operating systems and JREs.

Also, it’s good to consider that the normal Client-Server communication model of OPC UA does not make any requirements about deterministic behaviour. As an example, there’s no requirements that subscriptions should provide the exactly same notification message stream from the same measurements (for example sensor reading). As a second example, the OPC UA specification doesn’t mandate that write requests or read requests coming to the server even need to be handled in the order that they came in.

All this being said, if there would be only one client application which connects to a server and doesn’t use subscriptions, then the program execution should be deterministic in behaviour.