Quote Originally Posted by strelitzia View Post
I just looked at the auto_loaders file for both OPC and ECA

ECA is using $autoLoadConfig[90] whereas OPC is mainly using $autoLoadConfig[200]

I took a wild guess that perhaps ECA being loaded earlier than OPC was causing an issue so as a test I changed ECA to $autoLoadConfig[200] as well.
The issue went away, but not sure of the ramifications of changing the loading order like this.

Is it likely to cause issues for ECA, or should I perhaps change OPC to load earlier?

What do you advise Cindy?
You didn't indicate in your original posting, @strelitzia, but are you, by chance running zc157?

If that's the case, there's a bug in the zc157 core, identified by @mc12345678 (https://github.com/zencart/zencart/pull/3654), that prevents multiple observers from watching the same event.