Did it work in older version? If you have not tested in older version to verify if it is an issue then the rule may just needs to be reworked.
Rules not working is something with the Context of your properties of how you defined it in the update rule.
For example: Let MainObject be the focal point all the time.
MainObject
|__Object1 (Collection)
|___Sub-Object (Collection)
|___Property = Foo <-- Display this when Property2 = ABC
|___Propert2 = ABC
The rule or the system needs to know where your context is (from what is current - is it top down or bottom up).
If you look at most of the update rule in the out of the box code, like you said above, try to see where the "focus" is or the "context" is on how it was applied with the hierarchy from MainObject. That is how you will get it to work or how you would debug why it is not working.
Hope this generic statement or fundamental helps you out. In short in all your example from the out of the box, see how it relates to MainObject (look at the properties of mainobject - which one are collection and which one are standard properties).
Workaround:
Some technique people used is to force a top level property to hold the values you want from MainObject.
MainObject:
|___Object1 (collection)
|__PropertyX <-- a temp holder on what you can pre-populate from the MainObject.
With using Update rule now it is much easier to force an update with the top level is where the context is.
Regards,
Mark Pe
SAP Senior Support Engineer (mobility)