Chart - problem when year is changing

Hi everybody, I have a problem concerning a column serie chart.
Everything is good when data occurs the same year but when there are datas on 2 different years the chart become completely wrong (see picture)DATES DATES%20OK
The X axis is YEARMONTH like 201907 / 201908 …
AppSheet understand that between 201912 and 202001 there are a lot of data like 201913 / 201914…
I have tried to change the type as Number / Text / Date but the result is always the same. I have tried also like 2019-07 but it is not working as well.
Is any one can help me on this topic.