Nassim Taleb also talks about this quite a lot: https://youtu.be/91IOwS0gf3g
TL;DR: while a single investment may be ergodic, portfolio management (the math behind weighting successive and concurrent investments/bets) is not, as it has a strong dependence on all prior states.
Ergodicity is less about memorylessness and more about the constraints on transitions into this or that state. A system is ergodic if "anything that can be an outcome, eventually will happen".
A million players each placing a single bet will have an expectation of losing the house edge.
A single player placing a million bets has an expectation of $0.
The fact that the aggregate and the single entity Experience different expectations despite both placing a million bets is what makes this ergodic.
One way for a process to not be ergodic in the mean is when there's some sort of barrier, as sibling comments allude to.
Another is if the overall mean value is picked randomly each time the process starts, but is different each time the process runs. So for example personal monthly expenditures are not ergodic in the mean, because some people are born into circumstances that make them wealthy, and they will on average spend more each month than people not born into such good circumstances.
The ensemble average will tend towards people's average spending, while the temporal average will tend towards each individual's spending.