Library reference survey block not in survey flow

I wouldn't advice using this approach even if you get the desired results, primarily for the reason that you will not have access to the randomization order in the reference survey in your data.
You're getting not in the survey flow probably because there's an end of survey element in your reference survey, which doesn't just mean end the reference survey, but the entire survey, i.e. your respondents won't come back.

Thank you for the swift answer, ahmedA!
With not having access to the randomization order, do you mean that the output data file will not show the order in which blocks appeared (which would not be a problem for this survey), or that the randomization simply won't work for the survey at all?
As for the reference survey, it does not contain an end of survey element. Could there be any other reason for the 'Not in Survey Flow' label?
Again, when I run the survey myself, everything works as it should (including the randomization). So I'm a little confused 😅

Since we don't have access to the order of randomization, we can't be certain that the randomization took place in the reference survey. Theoretically it should, but like I said, the absence of data casts doubts on it.
I had used a similar approach for one of my studies, and once I deleted the end of survey elements from the reference surveys, the not in the survey flow markers disappeared. This was around 3-4 months back, so probably, they've made changes to the internals.
I suggest getting in touch with the support team for an answer. Please share the explanation they provide.
Thanks.