My project originally used version 2.0.x, but recently switched to 2.1.1.
When using the new version, I found that the interface refresh lags when calling functions like moving the canvas or zooming with QCustomPlot. This includes the lag when moving the cursor lines that I drew myself. I tried blocking my own mouse events and only testing the underlying QCP, but the lag persisted.
While inspecting the source code, I noticed that in the QCustomPlot constructor of the new version, the line setAttribute(Qt::WA_OpaquePaintEvent); was removed. After I re-set it, the interface refresh no longer lags.
I'm not sure what caused this issue. I hope to receive official feedback on this matter. Thank you!