I found, that when you repeatedly instantiate PlotItems and delete them again, the corresponding QMenu objects for the context menus of the plots never get destroyed. I saw lot's of QMenu instances using GammaRay (https://www.kdab.com/development-resources/qt-tools/gammaray/)

But this can simply be reproduced with the following snippet. The more often you create, add and remove new plot instances the more memory is used. Simply increase N to e.g. 100, 500, 1000, 2000 and check the memory usage.

import pyqtgraph as pg

app = pg.mkQApp()
widget = pg.GraphicsLayoutWidget()
widget.show()

N = 10
for i in range(N):
    plot = pg.PlotItem()
    plot.plot(x=[0,i, N], y=[0.0, 1.0, 0.0])
    widget.addItem(plot)
    app.processEvents()
    widget.removeItem(plot)

if __name__ == '__main__':
    pg.exec()