Hey Greg. First, let me clarify that I am neither with ONC nor the SITE test tool team, so I can't speak authoritatively on this matter. I am just one of many implementers.
But I have been around a bit, currently as an EHR regulatory consultant with Chart Lux and prior to that EHR Testing Director at Drummond Group so I have been dealing with CCDAs and CCDA interoperability for 15 years now, which is why I'm active on this list and offering comments to assist but also to still learn.
One thing with the CCDA specification is that it is very flexible, due largely to it being an "open template" design where we can add additional sections at places and also having options to place data in different locations. But that can hinder interoperability which is why the original CCDA Companion Guide came out back with the 2014 Edition FR release when it was simply "best practice" suggestions and not official compliance requirements. Since then, ONC has turned the Companion Guide into a requirement along with the main CCDA IG, and the CCDA IG vs 3.0 fully merges the core IG with the Companion Guide requirements because of how important interoperability is.
All that to say, even if you could insert the Planned Procedure in the Assessment and Plan section per the flexibility in the main CCDA IG, I can understand if it is rejected by ONC/SITE test tool because of an interoperability concern as I don't think the combined component section is the "common" method of implementation.
But, the tool is not absolute and it can be changed, and that is why we present questions like yours here. Looking the specification, I would agree with you that Planned Procedure could be in the Assessment and Plan section (2.16.840.1.113883.10.20.22.2.9:2014-06-09), and given the HL7 authors have kept both combined or separate options available, I think the tool should accept the Planned Procedure (2.16.840.1.113883.10.20.22.4.41:2022-06-01) in either of those component sections. But the test tool team and any ONC liaisons would need to weigh in on this. They may have better reasons for not doing that.
Finally, to Brett's recent email, and this is for everyone posting questions here, always include your CCDA that is creating the error in the email in question , if possible. Debugging or even analyzing CCDA questions is something of a dark art as much as science, and seeing the specimen at hand greatly helps make for a better response.
Kyle