Didn't want to create a new topic since my issue is very similar. Except that I don't use GNOME.
Running the latest version of Geany on antergos with KDE Plasma. Super-often, I also experience lag (which takes about 1 second or so) which occurs during any of these actions:
switching between files; scrolling text up/down typing text; cutting/copying/pasting text; and doing anything else which requires updating (refreshing) displayed content;
In other words, it takes about 1 second (maybe slightly less) for Geany to update displayed content, which drives me crazy, since Geany is the only normal text editor I found as Notepad++ replacement (coming from Windows world).
So far, Geany is the only app on my computer which has this type of lag. Running the latest generation of Intel i5 8400 6-core CPU with integrated GPU, 8 GB of RAM, and NVMe SSD, so it's surely not performance-based issue.