Talk:Gold Miner/@comment-162.233.17.79-20141213062422/@comment-27151764-20160828153515

At the list of known issues - [[Link]https://community.callofduty.com/t5/Call-of-Duty-Heroes-General/List-of-Known-Fixed-Issues/m-p/9915297]

It says "Gold/oil/diamond miners stop giving resources for a short period after being upgraded (this sometimes includes boosts)"

Not noticed it myself (iOS), but you can try closing the game and restarting?