refitting already fitted model

I have declared and fitted a model with the following code:
model= Prophet(weekly_seasonality=False, daily_seasonality=True, changepoint_prior_scale=0.5)

and i add 4 regressor
model.add_regressor('regressor1')
model.add_regressor('regressor2')
model.add_regressor('regressor3')
model.add_regressor('regressor4')

i follow rules in "Updating fitted models" section at link: https://facebook.github.io/prophet/docs/additional_topics.html#flat-trend-and-custom-trends

But **sometimes** i try to use this function to refit a new model the following two error pops up:

1. **mismatch in dimension declared and found in context; processing stage=parameter initialization; variable name=delta; position=0; dims declared=(3); dims found=(25)**
2. **invalid index to scalar variable** - this happens in function **stan_init**

Can you help me to understand what are the problems?