No. An integer getting deterministically set to an unintended value is a bug. A bug is not the same thing as UB. (Even if it were non-deterministic, it would still not be anything like UB.) It's not the same ballpark, not even the same sport.
What if the wrapped index is used to construct an invalid pointer? It might be possible, not sure. What if the integer is used to read the wrong data from disk, or corrupt data on disk by writing to the wrong location?
What if the wrapped index is used to construct an invalid pointer? It might be possible, not sure. What if the integer is used to read the wrong data from disk, or corrupt data on disk by writing to the wrong location?