Does your Nucleofector Solutions contain anything that would inhibit attachment of adherent cells?
In many cases where decreased attachment is a problem, the cause is inactivated trypsin. Unless the trypsin is inactivated with trypsin inhibitor or media containg BSA or serum, it will continue to degrade the cells and ultimately decrease cell viability. As a general rule, as soon as the cell monolayer begins to detach, add media or trypsin inhibitor to the culture dish. Alternatively, one can use a cell scraper to detach the cells.