The bug is that on Fortune Island, all seasonal events show up as completed, even though the season just changed and you did nothing to complete them. Only stunts are available for completion.
This is not “my” workaround, I have read it on these forums and tried it out and the guy was right. So this is not my credit, I just want to help, but I cannot find the name of that guy (edit: found the guy, credit where credit is due… everyone thank S4nch3z):
Before season change make sure that you are on Fortune Island. When the season changes and you are online on Fortune Island, all events will be available uncompleted. S4nch3z said that once you go to mainland and back, the events are completed, but this did not happen for me. They stayed uncompleted and I could do all of them. But before I switched, I did one of the events, so maybe that was the reason.
Yay @S4nch3z , I can finally do Fortune Island events again.