I have a good news! I have performed reconditioning procedure with one of the BME280 which had positive +7% offset and now it reports almost the same humidity like the reference HIH4000 in the range between 10% and 50%RH. I performed dry-baking at 120 centigrade for 2 hours. I could not control the conditions dyring rehydration. But i suppose that air temperature was close to 18 centigrade at ~70-90%RH for ~8 hours. For rehydration i used compact desktop air conditiner integrated with air humidifier. Hope this information will be helpful for those who have faced with the same problem
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