Likely answered this before, but it still keeps coming up:

If you’re making reductions and also seeing an optometrist, you may at some point get a ‘diagnosis’ of some new astigmatism.  Or you might notice some double vision / ghosting after a reduction, possibly just in adverse lighting conditions, ie. dusk, evening, artificial light.

Don’t get cylinder correction for that.  Just don’t reduce again until the effect is gone.

More in this video:

Hopefully useful!