Hi It is very possible that your tomatoes have fusarium and verticillium wilt even if they are listed as being VFN resistant.
One of the major causes is planting the tomatoes in the same spot year after year.
You should rotate they area where they are planted each year to keep this from happening.
To tell for certain if your plants
have either one of the diseases, take a vine and make a diagonal cut, (the longer the bias the better) then look for discolorations inside the vine. It usually shows up as a darkened area. This disease is basically the same thing as hardening of the arteries in a human. You can treat it with a fungicide, this will help slow the spread of the disease down, but it will not cure it.
If you have only a small gardening area and crop rotation is not possible try growing
them in raised beds,planters, or pots, using fresh potting soil each year.
Hope this helps