Since 1.19.4(and maybe since earlier snapshots), the behavior of the jukebox has changed, there will be a particle effect on top of it while it is playing back, and the disc will automatically dropped to the hopper under the jukebox when it finished playing back. But when you are using a resource pack that replaced the stock disc audio, and the customized one do not have the same length with the stock one (typically longer), the disc will dropped to the hopper before it being fully played back, and the audio of playing back will also be stopped with the dropping happens.

I thinks in the current version, every single time as a disc entered the jukebox, the game will start a countdown depends on witch disc you've put/dropped into the jukebox, and as the time is down, the game will stop playing and drop that disc out, and this is imperfect.

From my opinion, the action of stopping the particle effect and playing back, combined with dropping the disc out to the hopper should be some how related to the audio playing, for example like making them as a callback and call it as the audio thread really ended up playing(which could cause a desync between server and the client, not good), or just get the properties of the customized audio file inside the resource pack from the server side, and set the delay of the dropping action(the countdown) match the actual length of the audio being played, so that every client loaded with the proper server resource pack should behave perfectly.