Question -- afterward, are you solving the problem by pulling down more cable in the pinch bolt?
If yes, than odds are that either the cable head is slowly coming off, or pulling through the lever cam, or the housing is extruding through a ferrule, or at the lever. The other related possibility is that you didn't properly seat the housing in the lever before taping your bars, and the housing is slowly creeping forward toward the lever, effectively getting shorter.
This is a classic "raise the bridge or lower the water" scenario. Either the wire is getting longer, or the housing shorter, and a bit of tracking down will verify which and where.
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FB
Chain-L site
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