I recently ran into this problem as well. I have a layer from AGO that contains a field with a text length of 2500. Currently there is only one row with > 255 characters in that field. That row isn't exported using to_featureclass method and generates the following error.
It doesn't matter if i overwrite or sanitize columns, i always get the error above. The field in the resulting feature class has a length of 255 which seems to be the cause of the error.