Need Help with Preparing Mouse Blood Leukocytes

I have a unique situation and I need some guidance. We are trying to label 5
uL of whole blood (Heparin treated) collected from the saphenous vein (we
actually collect 30-40 uL and then split it up). We ran though this last
week and used RBC lysis buffer from a company called eBioscience. We used
400 uL of RBC lysis buffer with 10 uL of stained cells (5 uL blood, and
antibodies to 10 uL). We lysed for 5 minutes and found that when we tried to
analyze the samples, we just got what looked like a bunch of RBCs on the FS
vs. SS plot. We concluded that it is either actually RBC contamination or we
killed all the cells during the lysis step causing us to see only debris. We
have previously used this exact same procedure with humans without any
problems. We are able to make measurements on these small blood samples
because we are using a Gauva EasyCyte Mini. Any suggestions that anyone has
would be extremely helpful as we do not have extensive experience with mouse
blood samples.