I know of a notch that is around (?)581mhz. And also another at a lower freq. It is usually about .25db deep using stealth sweep. but usually I've found that if you have it on one span, you'll have more close by. So combined spans with the same notch will cause a significant amount of loss at that freq.
This is CABL.com posting #215340. Tiny Link: cabl.co/m4bo