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It sounds like it has become glazed/filled with "swarf".
To restore the cutting ability of a hone you need to lap it. For starters try 1000 grit wet/dry sandpaper.

Try simple soap & water first & a brush of some kind. That usually works.
Lapping is usually not necessary unless the sides are "high" /center is dished. Be sure to soften the edges of the hone.
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