Over the years there has been some speculation that BART elevateds would require a rebuild if structurally stronger and presumably heavier cars were indicated.

I also thought there may be some greater tendency toward horizontal and vertical oscillation with rubber tyred vehicles. Tires flex some but steel wheels do not. So you get a longer monorail train and it wants to "shake, rattle, and roll"?

And add on subsidence of the guideway support pylons and you get a thumpety-thump; certainly on the Seattle line. Perhaps that is not so much a factor on the newer monorails.

Sao Paulo had a tire problem recently with their #15 monorail line which took some months for Bombardier to sort out to put the line back in operation.

You have to wonder why Sao Paulo has not tried any light rail AFAIK; heavy subway, monorail and thousands of buses. Gigantic population and really substantial demand for public transport. Plus seems lots of recent refugees from Venezuela, etc. LaLa on steroids.