I solved the problem although I don't understand it fully.
The progression stopped, not after a certain cell type but after a scroll. In most cells I relied on an implicit accessiblityLabel so I didn't specify the labels directly.
In trying to solve the issue, I changed my cells so they all override the accessibilityLabel
property and specifically return a label. That made it work.
I suspect that it was caused by some sort of timing issue where a newly loaded cell didn't have its data loaded fully before being asked of its accessibility label.