I have tracked this down to the TrendChannel tool, and have reproduced the issue in a clean Ninjatrader installation 8.0.26.1 64-bit .
Steps to reproduce:
1. Open a clean chart of NQ
2. Draw a few TrendChannel objects
3. Flip the chart to 6E and flip back and forth between NQ and 6E
There are performance issues and eventually the chart will freeze and the platform will crash.

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