Airvisual behaviour : Quality index drops to one or zero for quite long time several time per day

I have set 3 airvisuals.
The third one (set to LaGrandeMotte in France) has a strange behaviour.
The value falls to 0 or 1 several times a day and quite a long time. If I go on iqair web site, the value is quite higher (depending on the air quality)

Thanks in advance for the ideas

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The graph is a 24h period

This morning the value in iqair
Airvisual (iqair) gives an index of 42 whereas IQAIR website gives 97
image

Hello,
With today version of HA, the location can be entered via the town name (instead of lat/long).
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(I change the location after 20.00 o’clock)
This is consistent with the web site :

==> I assume that with lat/long there is some extrapolation