Exceedingly long ferm time for washed yeast

Two of the most recent times I've used yeast I've washed I've experienced excessively long fermentation times. The most recent example is a Best Bitter which started at 1.049 and now, after 14 days in primary, is down only to 1.020 with consistent and rather rapid air lock activity for the duration of the ferment. This yeast is the 1st harvest from a yeast cake which produced a very healthy ferment of the identical beer. It is Wyeast 1099 (Whitbread Ale) so even at it's very lowest projected attenuation there is still more fermentation that should take place.

I'm assuming the problem is in the harvest since last time I used this yeast the ferm didn't take particularly long at all. Any hints, ideas, suggestions, advice, input on this problem? (fwiw, I follow the routine in Bernie Brewer's excellent "Yeast Washing Illustrated" thread https://www.homebrewtalk.com/f163/yeast-washing-illustrated-41768/.

How long did you let the first beer stay in primary before harvesting the yeast? I ask because if it was anything less than 7 days, you probably harvested a lot of dead/unhealthy/quick-to-flocculate yeast, which are less than ideal.

Also, did you make a starter?

DrawTap88 said:

How long did you let the first beer stay in primary before harvesting the yeast? I ask because if it was anything less than 7 days, you probably harvested a lot of dead/unhealthy/quick-to-flocculate yeast, which are less than ideal.

Also, did you make a starter?

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I harvested the yeast after the beer was racked to secondary which was on day 14. That's appropriate, no?

Yep, I made a starter following Mr. Malty guidelines. I wonder, though, if I misconstrued the recommendation from there since I was making a starter from washed yeast rather than from a vial or smack pack. The starter I made was 1.5L which seemed plenty big for an OG <1.050 pitched into only 3 gallons of wort.

Was the yeast active in the starter? This is a good indication of yeast health from my experience.