Decreasing baseline with 1260 Infinity II DAD

Hi everyone, 

I have a problem which I hope that you can help me with. 
Yesterday, we experienced a decreasing baseline when running samples with a gradient from 95% MQ water (0.1% formic acid) and 5% MeCN (0.1% formic acid) to 5% MQ water (0.1% formic acid) and 95% MeCN (0.1% formic acid) on our 1260 Infinity II HPLC. We also observed the decreasing baseline when running instrumental blanks (I have attached photos). We have never seen this before, and we have been using the method for a long time. 
The retention times of the impurities from the column remains the same, and therefore I assume that the pump is not the problem. 
I am new to this, so please let me know if there is something that I am missing!

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