Hi Keenan,
Thanks for contacting Syncfusion Support.
We have tried to reproduce the reported problem by using MaximumZoomLevel property. But we are unable to reproduce it. We have prepared a demo sample for your reference and it can be downloaded from below link,
Also, we can zoom out from zoomed level by using the ZoomOut icon of ZoomingToolBar.
If the issue still reproduces, kindly revert us by modifying the provided sample. It would be helpful for us to provide you a better solution.
Regards,
Devi