I'm curious about the CHAINED_EXECUTION_NODE_LIMIT property in custom.proper

There is a hard limit of 100 for this setting:
forum.appian.com/.../Post-Install_Configurations.html

Oh wow, that's terrible. We're on 7.3 so maybe that hard limit appears in in a subsequent release. It's not mentioned in the 7.3 documents. Thanks for the heads up.

Looks like it is valid for 7.3 as well: "The default limit is 50. The maximum value is 100. No more than 100 unattended nodes can be present in between two attended nodes that form a chain. This property cannot be disabled."
forum.appian.com/.../Post-Install_Configurations

Gotcha. I was looking here: forum.appian.com/.../Configuring_the_Process_Engine_Servers. Thanks again.

To be honest,

We've bumped up against the 100 limit before as well, but always found ways to reduce the number of nodes on the chain. Determine what causes race conditions, and which nodes might be able to split off into a parallel asynchronous sub-process call. Many script tasks can be combined, if they don't have inter-dependencies. Worst case, you have to add a task partway through the chain with some instructional text that the user clicks past, but hopefully that is avoided. You might also consider whether this should be a wizard, or if they should receive the task on the dashboard/tasks list when it's available, or as a related action.