Blackjack Switch - Variance

Are there any maths whizzes around that can work out variances and standard deviations for BJ Switch (playing optimal strategy)? I've had some crazy swings on this game and maybe its a lot more volatile than I give it credit for. The last run is probably the worst of them all so far. I'd like to roughly work out the likelihood of a run like this. Playing it it just seemed like the dealer was constantly hitting 20 or 21 no matter what card they were showing. Pushing 1 hand was the best I could do a lot of the time. On a game with a 99.87% RTP this must be pretty unlikely. Screenshot below. Stakes were constant 100 per hand (ie 200 per round prior to splits/doubles)
 
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