That depends of what exactly is that anomaly. If your GNSS receiver tracks 4 satellites from the same constellation then obviously, this kind of ionosphere anom

That depends of what exactly is that anomaly. If your GNSS receiver tracks 4 satellites from the same constellation then obviously, this kind of ionosphere anomaly will with some probability lead to some kind of unexpected fix error (but with some high probability still smaller than the specified error of such receiver). I believe that typical somewhat modern multi-constellation GNSS receiver will either consider satellites affected by that as invalid outliers or just average that out.