Abnormally increased value in prediction section

Hello!

I'm using prophet to predict future sales.

In input data, the sales volume treated with squared root is used as 'y' value.
And cap and floor are each 100 and 0.
Additionally, price information is added with `add_regressor`

But some of the products , its result seems strange.
The value is increasing abnormally in the prediction section.
There is no holiday event on the prediction section.

Below is the example & input data.

### sample graph


### Input data

ds | y | price | cap | floor
-- | -- | -- | -- | --
2020-11-01 | 3.464102 | 970.0 | 100.0 | 0.0
2020-11-02 | 1.000000 | 970.0 | 100.0 | 0.0
2020-11-03 | 3.000000 | 970.0 | 100.0 | 0.0
2020-11-04 | 3.000000 | 970.0 | 100.0 | 0.0
2020-11-05 | 3.741657 | 970.0 | 100.0 | 0.0
... | ... | ... | ... | ...
2021-10-21 | 2.449490 | 990.0 | 100.0 | 0.0
2021-10-22 | 2.449490 | 990.0 | 100.0 | 0.0
2021-10-23 | 2.236068 | 990.0 | 100.0 | 0.0
2021-10-24 | 2.449490 | 990.0 | 100.0 | 0.0
2021-10-25 | 1.732051 | 990.0 | 100.0 | 0.0

### code

```python
model = Prophet(
growth='logistic',
holidays = holidays
)
model.add_country_holidays(country_name='KR')
model.add_seasonality(name='monthly', period=30.5, fourier_order=5)
model.add_regressor('price')
model.fit(data)
```

Why is the happening?