As stated in your docs, the applied ownership rule is the last matching one from the rule list. However, when multiple frames in my stack trace match with multiple ownership rules, which frame will be considered when deciding on an ownership rule?

The order of your matching frames does not matter in this decision, only the order of your ownership rules. So, if one rule matches the path on ie. frame 0, and another rule matches the path on frame 1, we will use the last matching rule in the order they have been saved in your ownership rules settings.