tree fern care

I have 4 large tree ferns, all in pots in the garden. I give them all a seaweed feed during the summer, water them very well and wrap them in duvets over the winter. Three of them have numerous fronds, look extremely healthy, sending many new fronds each year and I am delighted with them. Despite receiving the same care and attention the fourth one hasn't sent any fronds now for 3 years. It does not look dead though. There is a lot of brown "fur" around the crown and no sign of disease but I haven't been able to feel any frond formation in the crown . Is it likely to ever send fronds again? Has anybody ever had one which has stayed dormant as long as this? I have tried moving it to different parts of the garden it is currently in a shady position but that hasn't made any difference. I will be wrapping it up again this winter, in the hope next year might bring an answer!!