I think that the predator foxes and prey rabbits have been labelled the wrong way around, reminder to switch them :). I think the rabbits are x and foxes are y. I think it is in the description of Activity 3 in Week 3 and it appears in the plots.
I think in Activity 1 in Week 4 lab sheet not solutions, in the forward euler derivative there was a typo in the derivative of previous time point, it used the current time for x instead of previous time : time-self._delta_t.
(In the solutions it is correct though because it has variable old_time, so please don't change this! :) )