I have a 30" HP ZR30W (resolution 2560x1600) and a 24" Eizo ColorEdge CG248 (resolution 3840x2160).
Until recently I've been able to use Premiere just fine despite the disparate resolutions between monitors. However as of 2 or 3 updates ago any Premiere windows I drag to the 4k monitor have a super tiny UI. My typical workflow is to have Source, Program and Timeline on the bigger HP 30" in front of me and all my other windows (Project, Effects, Audio Mixer, History, Markers etc. etc.) on the 4k Eizo monitor to my left. Lately this has meant that all of my project bins and files are these teeny tiny file names and ui text making it difficult to read/see.
This only happens in Premiere. Other programs work just fine with the 200% scaling set by Windows. I've tried messing around with the program compatibility (Change High DPI) settings and the High DPI scaling override but can't seem to find a setting that works to conform both monitors.