I've had a different problem. I have had the event twice in this game, about 30 turns apart from each other and the first time I didn't have the Soil Enhancement tech researched yet so I didn't see any effect and I did check that my planets had -90% manufacturing ... didn't notice if the malus went away after 10 turns but I didn't seem crippled much so I guess it was all good.
Then I researched the Soil Enhancement tech and was able to use it once on all my planets ... wasn't sure if that was due to the first event or not.
Then I had the even again and once again chose the 1 free tile on each planet for -90% manufacturing for 10 turns. Before that I had enhanced most of my planets and couldn't enhance further. After the event, I could enhance the soil on my planets one more time.
The bug I noticed tho is that about 25 turns later, I still have -180% manufacturing malus on all my planets (like two events stacked over each other) and it doesn't go away !!
I'm almost thinking about continuing this game anyways since it is still fun 