all mobs and items change after update

hello i hope u all have good day,

i need help! so i update my server from 1.14.4 or 14.2 to 1.15.2,

i click install on vanilla 1.15.2 and forge 1.15.2 and after i start server i se the damage!!

all mobs and items are changed! sheeps turn in to fish! and there was ender dragon in dungen!!!!!

and all items in storage changed!

so can anybody help me to fix it? i will very thankfull

ty for Answer.

i use vanila 1.14.4 and change it to 1.15.2

than spigot 1.14.4 to 1.15.2

than forge 1.14.4 to 1.15.2

after that i run server and all mobs changed

i did not know that.

and i did not change from vanilla 1.15.2 to spigot 1.14.4.

from tha start:

me and my firends make server on vanila 1.14.4

than we play like 2 month

and than my firends instal forge 1.14.4 and spigot 1.14.4 and some other mods on server

and than we play littel more on server...

after that like 3 or 4 day ago i go on server settings and press install on:

vanilla 1.15.2

forge 1.15.2

spigot 1.15.2

and than i run server and see all mobs change. its all the story

and thats my fult i didnot have enough knowledge abut install order and updating server

sorry if i not explaing it right

idk but server dont get reinstall.

so is there a why to fix mob problem? witout reinstalling server

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i check again and i think i dont install spigot at all, sorry it dont have install check mark on it