Thanks, @Alexander H. I check a few messages and don't have that info at purepath level, Could it be since the message type is TextMessage?
We are planning to do Load Testing in some queues to see how much can the MQ handle. Sadly is something that we might want to chart per queue in the future and not depend that OA is installed.
The message length is limited by the queue manager. The default max message length is 4MB. This max message length will be available via extension and also chartable. The OneAgent captures the message length (size) per transaction, without the OneAgent it's not possible to get transactional data. We've planned to make the message size available via request attributes, so that you can also chart and filter it.
It's hard to say why the message size is missing in your case. A deeper analysis would be need here, probably the best approach would be to create a support ticket for that.