You misunderstand. A loot table for cave spiders already exists. There is one for every mob in the game. The issue is that the cave spider’s entity data points to the loot table for the regular spider mob, not the cave spider.
I know in vanilla play that it is not a noticeable issue. But it is still an error and affects addon pack creators (such as myself). I created an addon that specifically tweaks the cave spider loot table, but doing so has no effect since no mob is actually linked to the existing cave spider loot table.
Happens to me and my friends all the time too! So annoying.
I have noticed however that for the times where it doesn't happen, when I dismount my horse I suddenly see it disappear and move super fast to where it should be (beside me) as though it had just teleported. All of this happens in like a split second but I do see it sometimes (especially when travelling great distances). I have a feeling the horse "disappearing" issue might have something to do with this mechanic.
Thanks for the suggestion. I have implemented this workaround and it works🙂 Though I do hope the vanilla behaviour file gets officially corrected in a future update so that creators won’t need to include our own fixed versions. Thanks for your quick and useful response!