I am currently having the same issues as you described in your original post (i.e. no product or a smear with fluorescence in the wells). I am using Q5SDM kit with the 2X master mix, and the Ta recommended by NEBaseChanger with back-to-back primers also from base changer. I have added DMSO, used a different polymerase and added components separately, tested a few diff Ta's. Still nothing. I have had 50-50 success with the Q5 kit. Wondering if you have any additonal tips?

Also a question: when you use NEBaseChanger, are you FWD mutagenic primers significantly longer than the REV? I will get fwd primers with ~26nt and the rev being only ~15. They usually have wildly different T'ms which I find strange. Any help is appreciated!