I've seen in a few cases where buffered triggers do nothing for late joiners. In one case, the instigator needs to leave for the buffered trigger to properly buffer for late joiners. In other cases, after 96 buffered triggers, all remaining buffers fail completely.
Example world: wrld_37443b7e-2bc5-4f1b-82e1-7c81f384b601
This world has 256 buttons that are always buffer one. There is an additional button that presses all of them at once. Clicking all the buttons and having another player join results in the first 96 buffer and the remaining 160 do not trigger at all. So... if your world has more than 96 buffered triggers, late joiners are guaranteed to not be synced!
World was original for another canny post. https://vrchat.canny.io/bug-reports/p/deferred-triggers-break-execution-order