I dont think its swiftgro, that may just be a coincidence. Ive had money trees grown under the swiftgro and on their own in the open and both have gotten bugged at some point. You can see that the tree is ready for harvest but it does not harvest.
I do know that I did not have this issue in November as thats when I started playing again after a long break, and I had money trees then that I harvested until they died.
I have certainly noticed this problem in the last couple of months though, so it may be one of the recent patches that have caused the issue.