Bluetooth signal seems to be deteriorating?

I have a monitoring system at home with 5 Ruuvi sensors.
This monitoring ran for 3 months without any problems. Suddenly my ESP32 had problems to receive the Bluetooth signals from the Ruuvis, although absolutely nothing was changed. Only when I positioned them differently, it worked again. How should a Ruuvi be placed so that it transmits best?
Does anyone also know these problems?

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I think most likely scenario is that something else is disrupting the 2.4 GHz band, for example a new wifi router or air moisture if tags are outdoors.

In general, RuuviTags have their strongest signal directly upwards on the side where the gore sticker is. Ruuvi Gateway has strongest reception in a donut shape, to the sideways of the antenna.