I understand your logical reasoning with this and I always appreciate and applaud such thinking-through. However, if it was software clogging up (I suspect you’re thinking of something like the old windows and Mac “memory leaks” etc then everyone around the world who’s on the same firmware version that your prime 4 is on, would all be experiencing the same behaviour that you’re seeing. As they’re all not… then it’s got to be a different cause at the root of your issues as it can’t (for the reasons outlined above) be the firmware (assuming you’re not on a really old firmware version)
So, I’m intrigued now… and I’m wondering about what you might use which maybe not lots and lots of the other users use… for example:
• Do you power anything from the usb ports on the Prime? Something which might draw more power, three hours into the night (or maybe you don’t plug it in until you’re three hours in… like charging something up iPad/iphone
• Do you run lighting from your Prime ?
• Do you record audio on your Prime 4 ?
• Do you do anything differently after 3 hours - eg: more streaming in of requests (tidal gets laggy at busier times) once the dancefloor gets going? Play shorter tracks/edits? Play longer mega mixes after 3 hours?
• more scratching after three hours?
• more use of fx after three hours?
• if you’re on wifi music streamed in, rather than local stored music , does the venue have more public (also sharing the WiFi ) after three hours ?
Also, it’s worth trying an ssd which many other users on this forum use - the Samsung - if it doesn’t have the same lags that you’re experiencing after 3 hours now, then it might be something temperature or cache based on your Crucial drive - crucial are well known of course, but who knows, they might use some sort of cache which fills up after a few hours
Some food for thought maybe