7 I think you have discovered a bug, and you got already an excellent workaround. However, here is another way to obtain this result, which might be even a bit shorter. More importantly, the fact that this method works may allow us to come up with educated guesses on what's going on. All you need to do is to ["repair" the `\pause` command](https://topanswers.xyz/tex?q=1126#a1350). I do not want to repeat all information from the linked post, but the `align` and so on environments "run" the code twice, one time in a "measuring" phase and then "for real". By suppressing the measuring phase in `\pause`, your issue gets solved, too. This seems to suggest that the `\smashoperator` uses the "wrong" boxes in the subscripts of the sum.
About TopTeX 78 21
6 This is merely to honorably mention the amazing `circledsteps` package, which is written by an [amazing squirrel](https://topanswers.xyz/user?id=809&community=tex). :smile_cat: It seems to me that you have reached the point at which you might want to use the circles inside nodes of a `tikzpicture`. However, this prevents you from using a `tikzpicture` for creating these circles as this would mean that you nest `tikzpicture`s (unless you want to use `\savebox`es or play Russian roulette). On the other hand, with the circles created by `circlesteps` there is no problem. (I also think that these circles compile a tiny bit faster, but this is almost impossible to measure.) Then you can use the `matrix` library to create the tables, and to relatively align them to each other.