I managed to resolve my issue, but am still unclear about whether there would be a way to fix this within Mathematica or how this issue arose to begin with.
Exiting out of Mathematica completely, using my display control panel to "incorrectly" rearrange my display locations, restarting Mathematica (and confirming that it had updated to the incorrect locations), exiting out of Mathematica, using my display control panel to correctly arrange my displays, and then restarting Mathematica seems to have fixed the issue. Effectively, forcing Mathematica to recognize that my screen locations had changed and to update settings to reflect this change. I would hypothesize that some configuration setting got garbled, but is only updated if Windows flags display locations as having changed.
I would love to know more if anyone happens to have a better answer! Similarly, I'm nervous about this issue reappearing, given that it took few moments to go through the above process, rather than simply updating some system setting inside Mathematica directly.