You are sampling the output voltage of the DC-DC converter with a resistive divider?
How much capacitance do you have at the input of your amplifier ?
This will form a low-pass filter. Your error amplifier will also function as a low-pass filter with gain. Are the two time constants similar ?
if not, take the dominant time constant as an estimate.
Your ramp will appear at the output amplified (I assume, depends on your circuit,
what input voltages, reference voltage, what output voltages) and delayed by the time constant of your low-pass. Later stages (comparator) usually contain some form of sampling of this output (the delayed and amplified ramp), such as a latching type of comparator, for example.
Hope this helps.