The script won't work with unavailable or too many assets in the list. So it's no good idea to try downloading all assets from some list, unless it was checked before that all can be really downloaded. Otherwise the IB API can disconnect.

"Though IB has lifted the "hard" limit, we still implement a "soft" slow to load-balance client requests vs. server response. Requesting too much historical data can lead to throttling and eventual disconnect of the API client. If a request requires more than several minutes to return data, it would be best to cancel the request using the IBApi.EClient.cancelHistoricalData function".