Open GL error after adding new 4K monitor

That's it. The only thing that changed is that I switched from a 1080p monitor to a 4K monitor. Software versions, card, cables, everything else is exactly the same and the app was working perfectly immediately before I swapped in the new monitor.

MacOS 10.13.6, Character animator 3.4, GTX 1070ti, Nvidia driver 387.10.10.10.40.195 (up to date)

The monitor is well within the capabilities of the 1070ti

rebooted, reinstalled, no other apps, trashed prefs, the whole nine yards

seems like adding a new monitor shouldn't break the app, yeah?

Any help is appreciated.