There were some code breaking changes from 8.0 to 8.1. For example, If you are using any vendor indicators, the "location" where your MachineID would be referenced in the vendor licensing would be different--that's something you would need the vendor to update.
Old location: NinjaTrader.Cbi.License.MachineId
New 8.1 location: NinjaTrader.Cbi.UserEntitlement.MachineId
Any "old" vendor indicators would be looking for a location that doesn't exist.
If they're open source indicators that aren't working, you would need to post the errors that you're receiving--you can export the errors from the NinjaScript editor.
To get the most accurate backtest in NinjaTrader you either need to use high fill resolution, 1 tick backtest, or code the strategy to use 1 tick data to fill orders.
https://ninjatrader.com/support/helpguides/nt8/NT HelpGuide English.html?understanding_historical_fill_.htm
It's the same calculation between ta.ema and the NT EMA. In NinjaTrader, if you don't set your calculation to OnPriceChange, the current bar is probably different. I just tested and I get all the same results for historical bars between the two (I only have realtime on NT and not TradingView).
Anyone have the original files that they would share for t-rex, sumo pullback, solar wind rk, rev out scalping, zone gpt, or any of the other entry style indicators?