Consider the measurement time in relation to the koff rate. Maybe you are working with a very strong binder and need to extend the dissociation phase. A technical reason might be the capture of autofluorescent dirt particles (often visible in the snapshots). Make sure all bottles, vials and microtiter plates are free from dust (if necessary, rinse them with water before use) and filter or centrifuge all buffers and solutions before use. If a malfunction of the buffer pump is the reason (no washout of analyte, which is visible in the raw data on both spots), please try to restart the device.