Editing a map created with PyQgis3 in Qgis Print Layout

Question

I create a new print layout using PyQgis and then I open it in the layout designer. Everything seems ok till I try to refresh the page or update the map extent, then map disappears.

project = QgsProject.instance()
lmg = QgsProject.instance().layoutManager()
l = QgsPrintLayout(project)
l.initializeDefaults()
l.setUnits(QgsUnitTypes.LayoutMillimeters)
lmg.clear()
lmg.addLayout(l)
page = l.pageCollection().pages()[0]  

lm = 20         # left margin
tm = 32         # upper margin

w, h = 900, 600 #width and height
page.setPageSize(QgsLayoutSize(1189, 841))  
theMap = QgsLayoutItemMap(l)
theMap.updateBoundingRect()
theMap.setRect(QRectF(lm,tm, w, h)) 
theMap.setPos(lm,tm)
theMap.setFrameEnabled(True)
theMap.updateBoundingRect()
theMap.setLayers(project.mapThemeCollection().masterVisibleLayers())   
theMap.setExtent(QgsRectangle(363600.0, 376800.0, 364500.0 ,377400.0))
theMap.attemptSetSceneRect(QRectF(lm,tm, w, h))
l.addItem(theMap)
l.updateBounds()

iface.openLayoutDesigner(l)

Answer 1

I found that the problem was with the map size 900x600 (I don't know why?) , so I solved it by initializing the map with lower size (half size in the example)

theMap.setRect(QRectF(lm,tm, 450, 300)) 

Then I resized it the disired dimension using attemptSetSceneRect method:

theMap.attemptSetSceneRect(QRectF(lm,tm, w, h))