I'm trying to cut/create polygons in QGIS 3.2.1 using snapping/tracing, but it only works intermittently - it will follow an existing vector line quite happily for a short distance, then drop it, then pick it up again some distance later. So I end up manually plotting all the vertices, which is very time consuming.

I have had no issues using snapping/tracing previously in this version of QGIS, but here I am using a PostGIS layer (in offline mode), so perhaps this is causing the problem?

I've tried tweaking the various snapping options, tracing different vector layers, saving/reloading etc but nothing seems to make any difference.

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    There are some issues with tracing. For example it needs to build an index for snapping to work. So if you load a WFS it will build the index for the initial extent. Then if you pan the map and get more features those new features cannot be snapped to because they are not in the index that was built when the layer was loaded. – HeikkiVesanto Nov 22 '18 at 17:55
  • Thanks #HeikkiVesanto, that certainly fits with my experience. – JimS-W Nov 26 '18 at 15:51

I've found that by enabling the various snapping options by default under Settings>Options>Digitizing, including 'Enable snapping on invisible features' I can get it to work 95% of the time now.

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