Greetings my dear exploiters!
There was a similar post about this, but i'll add a few bonus things so don't hurry to yell "Repost! Repost!"
As another memeber of this community posted, before you upgrade your MINE you should mine everything in it and then u get to mine it again...
I somehow got my mine and my herb garden reset when upgrading my garrison to lvl 3 when i had mined/gathered everything from them around 5 minutes before the upgrade, shared with guildies, tested works.
Please someone confirm if you can, because i was planning on posting this a week ago almost, but for some reason i couldn't make posts!
P.S. This is more of a tip than an exploit, but is also my first post! So i'd rather not start out grand and finish low :P