MQTT Engine initial tag values


I’ve recently updated my ignition instance to 8.1.30 from 8.0.16 and have installed the latest engine and transmission modules to match.

I’m seeing some strange behaviour with the edge node tags in engine. The initial value of the node metrics is null. They stay this way until I change the source tag value, then they will update. From my testing, this appears to happen with any new transmitter I create in transmission. Engine sees the node metric values as null until the value changes. Device metrics all come through as expected.
the screenshots below show a tag structure being published by transmission and read back by engine on the same ignition gateway.
There are no logs suggesting the message can’t be parsed, and forcing a rebirth has no affect. When I use an MQTT client and force a rebirth I can see the node metrics being published as expected in the NBIRTH message, so it appears to be something going on with Engine.
I also tested on another dev machine that previously worked which was on ignition 8.1.25, now on 8.1.30 and it is exhibiting the same behaviour.


Any help would be much appreciated.

This is a known bug in the MQTT Transmission module v4.0.17. We have a fix available in the latest Nightly version of MQTT Transmission if you’re capable of running a Nightly build in your environment. You can download the latest Nightly version of Transmission using the link below. If you cannot run a Nightly in your environment, you can go back to Transmission 4.0.16 until we officially release 4.0.18 with the fix in place.

Thanks Nathan, I appreciate the response.

It’s interesting that the bug is with transmission. When I decompiled the node birth message, all the metrics with values are in there as far as I can see.

Is there a scheduled date for 4.0.18?

Thank you for reaching back out. I was mistaken… I thought you had UDTs at the edge, but on further review I see that is not the case. You are not hitting the bug I thought you were. This looks to be a new bug specific to expression tags at the node level. We’ll look into this bug, but I cannot promise it will make 4.0.18 at this point. I will update this forum thread once we have a fix available.

Hi, I was wrong, this definitely appears to be a bug in transmission node birth messages. This only seems to occur if the tag being published is an expression tag. If I change it to a memory tag, it publishes the birth message as expected.
I have tested the following versions:
4.0.16 - expected value
4.0.17 - null initial values
4.0.18 - null initial values
This has caused us some significant issues, if you have any update available on a fix, that would be great.

I notice that on 4.0.17 the node birth doesn’t even include the metric values.

Hi Chris,

Thanks for reaching out. We now have a fix available for this issue in the latest Nightly version of Engine and Transmission (link below). Please let me know if you see any issues after installing this Nightly (if you can run a Nightly in your env). This fix will go out in the next official release of our modules (4.0.19).