Running the latest version of the now open source Surge (1.6.1.1) (available free here:
https://surge-synthesizer.github.io/) in Reaper 5.979 Linux (native) on Ubuntu 18.04 LTS.
Zoom settings above 100% (under menu in the bottom right had corner of the GUI) don't work properly (at least in Ubuntu 18.04 LTS). Here's the (correct) default zoom setting (100%):
(Image removed as issue now resolved)
but...
Selecting ANY of the available sizes apart from the default 100%, i.e. from 125% to 300%, results in this (the REAPER plugin window expands but the plugin's GUI is cropped):
(Image removed as issue now resolved)
The plugin GUI size doesn't even change between 125-300%.
(These zoom settings in Surge all work fine in Windows 10 with REAPER 5.979, BTW.)