Yap, or it is somewhat uninstalling it from your workshop folder, or just checking which addons are on place - it took time, the bigger file is and the more addons are in belowmentioned workshop folder in your comp, the more time it takes. Solving - or place already downloaded from steamcommunity map file from Program files (x86) (if u use 64 windows) or just program files\Steam\SteamApps\common\Left 4 dead 2\left4dead2\addons\workshop to addons folder, don't forget unsubscribe in steam workshop from that map, or it will be downloading all over again, or just download manually same file from http://www.l4dmaps.com/details.php?file=6905 and click on it - it will install itself in addons folder - again, don't forget to delete then map file from workshop folder on your comp and unsubscribe from that map in steam workshop.
Restart steam and the game after it.

It is better to move all addons subscribed in steamcommunity from ...\addons\workshop folder to ...\addons, as game when loading took time for checking which addons are on place - it took time. Do not forget in that way unsubscribe from those addons on steamcommunity, as it will be redownloading them if subscribed.

you have to many AdOns

Originally posted by Fungi375:

you have to many AdOns

late to the party,grandma.