@CookieW great question. I recently wrote a post on how things are *supposed* to work, can you review it and take a look at the FAQ section under SCCM scenario? The post is here: Understanding Office 365 ProPlus Updates for IT Pros (CDN vs SCCM). There have been a few bugs in the past but to my knowledge those have all been fixed, even in latest Semi-Annual Channel version.
Do you have any software packages in Software Center which change channels, call OfficeC2rClient.exe (not supported) or add\remove Visio or Project? The reason I ask is anytime you request a change, by default Office Client will always pull the latest build for respective channel from CDN. Due to customer feedback we recently added a feature called "MatchInstalled" which basically says, just do it but keep the same version of everything even if newer build is available. Is it possible these few machines are getting a configuration change we call "2nd Install" and MatchInstalled is not being used? This would explain observation.
One additional thought, "Monthly Channel release is supported only until the next Monthly Channel release is available." We think about Monthly in terms of customers using CDN with Delivery Optimization for this scenario because the number of builds released are very frequent. So while this has nothing to do with your question I wanted to make sure you knew support statement for Monthly. Customers who need more time\predictability tend to use Semi-Annual or Semi-Annual (Targeted).
Let us know if these are plausible explanations. If not, get in touch with MS Support who can gather logs and have in depth review.
