I was having the same problem with snapping and editing slowing to a crawl. I remembered having an issue with trace a while back and a previous forum workaround/suggestion was to fix the spatial index which in that case had become corrupted for some reason. So I decided to check the properties of the feature I was trying to snap to in ArcCatalog and saw there was no spatial index. Remedied that and now snapping is fully operational again. Not sure why the spatial index sometimes becomes corrupted (I'm not tech savvy) and new to Arcmap but it was a simple fix that worked for me. Hope this helps
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