What kind of phase do you have in your Proton spectra? Did the lock phase change, ... if so you may be sitting on a side band artefact of your deuterium signal! Is your sample salty? Are there parts of paramagnetic catalyst or metal catalyst inside? All this may be influence the deuterium / lock signal quite often.

If you have troubles with locking by such effects, the automatism and algorithm fails.

Now you can try to do it by yourself. First start with the doped H2O/D2O sample. This one should lock easily. ... keep z0 and lock phase and rise up lock gain and lock power to maximum, If you switch the sample, then you see the wiggles, ... move slightly Z0 until the wiggles go more and more less often, until you see only one signal as a step function.

Now you can reduce lock power and lock gain, until the signal does not fluctuate in its height and keep it around 70 to 80 percent of its level.

Have a nice try, Uli