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It likely is a mealybug infestation. Try spraying the plants with Neem oil.. These articles should help:

https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-pests.htm

https://www.gardeningknowhow.com/plant-problems/pests/insects/outdoor-mealybug-control.htm

Be sure to check for a pest as well, such as aphids, spider mites or scale. These articles should help:

https://www.gardeningknowhow.com/ornamental/flowers/gardenia/common-gardenia-diseases.htm

https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-pests.htm

So, I did all of the research I could, including pulling pictures of the building itself. I could not see any Gardenias, but I did see some white Viburnum in some of the photos. Some species can smell similar, and are hardy to zone 4. For example, Viburnum carlesii could look pretty similar in passing, and it does smell nice.

Checking horticultural databases in your area, and in known places where gardenia has been noted, I couldn't not find any reference to this happening. They have been noted growing on the edge of zone 7, but going down to zone 4 wouldn't be possible.

If there is a horticultural group there, maybe you could ask them about it. You could take samples up to your local extension service, as well.

The bottom of this article explaining about your local extension service will contain a search form at the bottom, as well. This will help you to find the closest one to you.

https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm

Those photos are rather dark, but the plant does look poorly. Pruning may help. Cut it back by about half. If any of the entire stems look dead, remove them to the ground. (or just above the graft if it is grafted) Normally this is done after blooming, but since that is an issue, go ahead and trim it now. You can give it some fertilizer now if you haven't yet this year. (Use a fertilizer for acid-loving plants and follow directions.)

Here is more:

https://www.gardeningknowhow.com/ornamental/flowers/gardenia/when-to-prune-a-gardenia.htm