Statement in "Release Notes" immediately above is incorrect. Setting "max_bars_back=2000" in top strategy line does not prevent possibility of exceeding 2000 order limit. It instead is used to manually define how many historical bars are preloaded for indicator calculations. If you receive an ‘out of depth at index’ error this means something in your script calculations requires a certain number of historical bars and for some reason those bars were not automatically allocated. Raising this setting may help prevent that error from occurring.
For preventing the error on exceeding 2000 orders you must take steps to reduce the number of trades. Various means to do this include changing the range you are backtesting, changing the period, changing the frequency of how often your strategy trades, etc.