There are several explanations to this phenomenon.
1. This could be due to Aqueous Normal Phase (ANP) HPLC and is a unique property of Cogent HPLC columns with Cogent TYPE-C™ silica. In this case the column is behaving normally.
2. If you know the mechanism is most likely to be reversed phase, then there is potentially a problem with your instrument.
Check your A and B solvents and make sure they are not switched and verify which solvent is in which reservoir. Go through the lines of each solvent and make sure they lead to the correct pump. For example, check that the lines are not switched at the degasser or going into the pump(s).
If your system uses a dual pump set-up, calculate the flow rate of each pump and make sure it is calibrated. Take a 5mL volumetric flask and time how long it takes for each solvent line to fill the flask. If one pump is not delivering accurate flow, this could be the reason.