Comparison between the LoTSS DR2 mosaics and the extracted and recalibrated images for the clusters Abell 1430 (top panels) and Abell 1294 (bottom panels). For both clusters, optimizing the calibration toward a nearby bright compact source improved the image quality. These errors in the LoTSS DR2 mosaics were caused by the spatially varying ionosphere. We note that the DR2 pipeline could have achieved more or less the same results with a different facet layout (but at the cost of reducing image quality in other directions).