The strange thing is that it worked some time ago. I have reworked my weather app completely and now I wanted to reactivate the widget and got the problem.
I used the old layout file and the old code. The only thing I changed was the data structure with the weather data and that I now use caching for the images so that not every bitmap is loaded again for each image.
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Ah, and I changed the image files. They now are 256x256 pixel in size instead of 128x128. I will try to use LoadBitmapSample instead with the size I need.
Thanks for the info. With this I can hopefully fix the issue in my app.