This is a common error. Please refer to this article and see if it helps  https://optics.ansys.com/hc/en-us/articles/8355464963987
If there is curved surface on a flat surface, you may move a little bit so they cut not are simply tangential.
Sometimes it can be version issue. Please upgrade to the newest version.
Or you may need to rebuild the simulation file.
Do not use too small the mesh size.
If problems still exist, please give some screenshots for the settings and geometries.
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