It was reported to me that slowpokes were not dropping anything when killed,
when i went about trying to test this i first started with /pokespawn and indeed there were no drops so my next thought would be to try boosting the rarity of the natural spawn to 300, time to day and change the biome to forest,
This is where i discovered that natural spawns were broken, after awhile i decided to do some testing after speaking with woppo and i basically replaced the external spawning json for slowpoke with one from 7.3.1, bascially removing all galarian spawning info, with the drops json i removed the form1 info as that is the galarian one, and i removed the form:0 line from the normal one,
once i did this i loaded back into single player and slowpokes were spawning naturally in the forest due to the changes i did with it's spawning, both the natural and pokespawned slowpokes dropped items upon death leaving me to believe that the galarian spawning and drops info was the cause after all.
After speaking with a few owners in the server owners discord, hutchy found out that it's the whole form thing that was the cause
Basically because it doesn't currently have forms /pokespawn spawns it with form -1 which doesn't have drops
Since i have no real knowledge about this stuff i'm taking his word for it but it does appear that it seems to be the case as a few others in the server owners discord have pointed out.
So basically if you remove all galarian info from the spawning json and the drops json, remove the "form": 0, line from the normal slowpoke drops, save and then load up the client/server it should fix all of this and allow slowpokes to start spawning naturally and give drops once again