I didn't save the replays but twice today, I've had my Pokemon switch before my opponents on a turn we both switched, despite my Pokemon being slower than their's. They were in gen7uu and gen6uu so maybe that has something to do with it but ye, here's a clear example:
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My Doublade had no Speed investment and the cress wasn't iron ball or paralyzed or anything. This can be a pretty useful tool in-game for determining the speed of foes, but it throws everything completely off if that isn't the case. The other time today, I assumed my max Speed Rotom-H was faster than the opposing Moltres, which came into play later in the game when it revealed I was actually slower.