I'm actually a bee keeper (very hobby level) and so I love the benefits, but do respect that there are times where we need to add antibiotics if we have problems. I love that it helped, but the recurrence suggests there is an ongoing problem that might need more aggressive treatment. We don't want infection to settle behind the eye or deep in sinuses or we could have bone damage and problems.
As far as what it is, if there was and is no wound on the face, the most likely issues are tooth root abscess or tumor.
Tumor is NOT likely if this came about really rapidly and further, I wouldn't have expected the propolis to have a profound impact (98%). So to my and hopefully your relief, I think this is infection.
Tooth root abscesses seed the facial bones beneath the eye and will decay through the sinus. Sometimes we get some nasal discharge, but that far back, most discharge into the sinus is swallowed. What we get is an acute swelling of the face that can go down from time to time as it drains out the eye opening or into the sinuses. The hallmark is that it recurs even if treated with meds (propolis, antibiotics, etc...) since the "root" of the problem, has not been corrected. In this case, literally, a tooth root.
We can try antibiotics, but will still expect recurrence down the road.
We can do dental x-rays to look, but this requires sedation and can be difficult to get or interpret in cats due to small mouth.
We can do a dental cleaning and explore the swelling, removing the likely offensive tooth and proving drainage, and then the game is won. If we don't find a communication between tooth and the swellling, we are already under anesthesia and can biopsy or debride if we think it's tumor... which I don't.
I hope this helps some. Please don't hesitate to ask me to explain further or touch on issues I might have overlooked.
Hoping Leann feels better quickly!
----- Dr. Will