Literally none. PMs are disciplined, there's top-down and bottom-up accountability, there's good transparency of work status and blockers, and people can take days off, miss meetings, and still contribute to decision making because all the work is done in a shared space that everyone in the company can see.

We don't even need standups most weeks because everyone knows where everyone is just by looking at the related tickets.

The closest things to "problems" are in bridging front-end design and back-end implementation collaboration because they use different tools, but that was at least as big of a problem when it was turning whiteboard mockups and Post-its into engineering tickets.