My hat is off to the designer (and perhaps the beta team) for I was unable to find any fault in the numerous triggers that service the two "Isolate the Ruhr Valley" objectives. From my knowledge of how they work, I can perhaps provide you with a few tips.
Here are the triggers:

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There are one set of triggers for the eight north Ruhr Valley victory points and one set for the south. Each objective is completed when the Allies occupy the corresponding eight VPs.
Here is the crux, though: The "-1" to the left of each trigger indicates that the trigger can be repeated over and over again. Note that beneath each "COMPLETED" trigger are sets of "OPEN" triggers that can be repeatedly fired. There is one "OPEN" trigger for each of the eight VPs addressed by the "COMPLETED" trigger.
What this means is, if the Germans retake
any of those eight VPs for each "Isolate the Ruhr Valley" objective, it is no longer completed (check marked), but turned back to open (question marked). As I said, this can happen over and over again, moving the objective back and forth between completed and open.
I looked at the AI teams and there appear to be at least three of them in which German units are directed to counterattack during the scenario. If the opportunity arises, these units will seize nearby VPs if they can, on their way to their ultimate objectives.
So here is what I think you need to do:
1) Realize that these are two separate "Isolate the Ruhr Valley" objectives and two sets of 8 VPs to seize and hold onto in order to complete them.
2) Keep referring to the mission screen to see if you have conquered all eight VPs in each set. If you don't see the check mark, click the question mark to be taken to the eight locations to see which ones you are missing.
3) After completing each "Isolate the Ruhr Valley" objective, periodically go back to the mission screen to make sure it stays completed! For, the enemy may have snuck back in and bagged one or two when you were not looking.
Note to officials: I would recommend that these "Isolate the Ruhr Valley" objectives be labeled as shown here:

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I hope this helps.