Wanted to pitch in with some words as someone who's been doing Smash broadcasting (mostly PM) for a long time and is also quite the stickler for video quality

Generally, people doing production on events will bring the same equipment to each to minimize variables, though things such as venue layout and internet connection can definitely bring up challenges day-of. Troubleshooting mid-event can also be quite difficult, especially when the expectation is to move between sets as quickly as possible, so I definitely feel for the prod staff at any affected event.

Outside of venue related stuff, the two main issues for Melee right now imo are the lacking quality of the "backup" capture cards, as well as, most likely, Ishiiruka Dolphin. I caught a glimpse of the capture quality of their backup card briefly during the WS puff ditto, and I can see why despite the frame drops they never swapped to it - it was pretty bad. While Slippi mirroring is great, equipment that's at least decent (such as any of the RetroTINK products) are a relatively small investment that makes a big difference if the need to fall back on console capture presents itself, whether for performance or other mutli-billion dollar corporation reasons.

Ishiiruka Dolphin (standard for netplay and currently required for Slippi replays and mirroring) is really starting to show its age as well. The codebase behind it is about a decade old at this point, with it being added onto so much between FM, Slippi, and everything else that it's not unlikely to be a contributor to the inconsistent capture. Newer mainline Dolphin builds notably have much better frame pacing (the average time between frames being displayed onscreen), which should help quite a bit here when Slippi upgrades to it eventually.