Positive RSSI values on MT7615E

Hello. I've recently been trying to set up DAWN between two openwrt APs (Redmi AC2100 and Archer C6) and although it is now at a point of kind-off may be sometimes working (I have seen my phone jump between 2.4 and 5Ghz, but for some reason most of my wifi clients would still connect to 2.4 and refuse to change network), I have found that some devices would have a positive RSSI value of 17, which in turn makes DAWN give 5GHz network a very low score and advice (?) clients to stay on 2.4Ghz. Is it normal to have these values (I have never seen them before, but may be I'm wrong) or is something severy broken?

(the same values appear in DAWN hearing map, even with networks that clients are not connected to, but I couldn't take screenshot of that)