Enabling non-printing characters display shows the problem with this file. You see, there is pilcrow character, i.e. paragraph character, in the field, which is considered to be a part of the field, but it interferes with the field logic.
I’ve created a file anew to demonstrate this:
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Here I have highlighted a field with pilcrow character outside the field:
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Here is field with pilcrow inside the file just like in your document:
First field updates automatically as nothing interferes with its logic, but the second one indeed produces the behavior you are describing. You just needed to start a new paragraph outside the field to avoid this problem.