Loudspeaker crossover network using Sallen key filters (MATLAB transfer functions)
I thought would cause both to have the same cutoff frequency so that when put together they would cause no gain loss across the system.

The definition of the cutoff frequency is not the same for all filters. For Butterworth it's the -3 dB point. But for Linkwitz-Riley filters it is the -6 dB point ! So you might think your filter is incorrect but it might just follow the LR-filter's intentions.

Also you should plot the Gain on a logarithmic scale, preferably in dB as that is the norm how Bode plots are made. And for good reason as it immediately tells you what order the filter is and where the cutoff point are.