Full disclosure: This issue happened in a game that was started before all seasons default to 20 days bug was fixed.
After I found the volcano, I've spend 2-3 days in it, exploring and collecting volcano specific resources. This was during the hurricane season. When I came back, at first, I didn't notice anything wrong. However, as the game progressed, I noticed the season didn't change when it should (easy to keep track when they all default to 20). I'm not entirely sure how much they are off currently, but I feel like it is a lot longer than the time I've spent in the volcano. However, I can't really be sure since I didn't specifically pay attention at the time. Sorry I can't provide more information, but I can provide the saved game if it would help.
1- Find Volcano. 2- Enter volcano. 3- Spend couple of days in Volcano. 4- Exit volcano. 5- See if the seasons switch when they should.