Hi
I wouldn't have expected the milk to drop significantly with such a small amount of solids.
Could it possibly be that she had a growth spurt and was taking much more milk and has now returned to a lower, stable, amount?
You could hold off from solids for a few days to see if her milk goes up again, missing solids out at this age is fine, there's no hurry.
Looks like you are offering at a good time, about an hour after milk feed. Morning is a good time too as it gives the rest of the day to see any reaction. Maybe move from 8.30 to 8.00 so there is an additional 30 mins for her appetite to build up in readiness for her next milk feed, it may make no difference but may be worth the experiment.