Running on a 1260 infinity HPLC vs 1260 infinity II HPLC

I have a method that I've run many times on a 1260 infinity HPLC that is now having separation issues when run on a 1260 infinity II HPLC.  Two peaks that I've always been able to get a resolution above 1.5 now barely separate enough to identify.  I've checked that the method is identical and tubing diameters and can't find any issues.  Does anyone have advice on what steps to take to determine how to run my method on a 1260 infinity II? 

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