This is a known issue with upscaling that we’re actively working on addressing. Please upload your original file here so we can run some additional tests.
In the meantime, try converting to a different file format and see if that helps. You can convert to DNG using Adobe DNG Converter:
We just released a fix for the grid issue in v2.1.1. It will require toggling off this Use Neural Engine button in the Upscale filter with Standard and High Fidelity model.
As the note says, turning off Neural Engine will prevent the grid artifact but can increase processing time.
Let us know if you have any questions about this and if it’s working for you. You can update to v2.1.1 in-app or by getting the installer here:
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