44cm fin sounds right for the board and sail size going from the Patrik recommendations.
patrik-windsurf.com/slalom/ I'd agree with the fin too soft theory.
Most of my 8.5m sailing is done on flat water either in a harbour or sheltered sea and you can get away with too large/small hard/soft a fin as its easy sailing but its when we get onshore winds things get interesting. I used to have a Falcon 125l*73cm and used it with a 47cm Select RS7 fin & 9m sail. The fin was a bit big but manageable. It also seemed quite soft and going over swells you could feel it bending and springing back as the pressure changed, lifting the board. To greatly exaggerate the feeling, it was like a pogo stick.
When I changed sail to a 8.5m it was definitely too big. I also has a 41cm which was ok when maxed, too small for lighter winds. Shortly after I changed boards to an older Exocet S4 125l (2004) and that came with a very stiff 50cm Select Superfast fin (also 2004 era). Too big for the 8.5m but tried it anyway, going over wakes of ferries (never used it on the sea), it was rock solid and stable. I bought a Drake 46cm DW (Down Wind) fin, as they are carbon and reasonably priced. Its between the old RS7 and Superfast in terms of stiffness and seems fine to me.
I've got a 38cm Drake Figure 8 Slalom fin for my 110l, its more upright and slightly wider at the tip. I've also got a 36cm DW as well. As you would expect the DW is slightly easier in the gybes and the F8 better upwind. I couldn't decide whether to for the 46cm in DW or F8, but settled for the F8. They were out of stock in that so got the DW.
I've also used the Select S1 (or previous versions) which are good VFM, but quite upright. The S1 (2015) is slightly more upright than the Drake F8. The current Selects seem to be higher carbon content than the older ones. The price of carbon Select fins has dropped since they have been building foils and can buy carbon in greater quantity. However, the S1 price seems to have gone up, implying the carbon content has also gone up.
My Exocet S4 is 80cm wide and OFO is 57cm, both wider than the Patrik 122, so it needs a bigger fin.
I also agree with the wind getting under the board theory.
The narrower Falcon 125l was easier in swell than the Exocet 125l, but not so good in light winds. Horses for courses.
Rocker lines & planing flat.
The S4 (2004) has a very short planing flat which gives a very responsive feel on flat water and lighter winds and makes it too lively for me in strong winds or swell. By then I can use my 110l Exocet S3 (2015). Its got a much longer planing flat. I've only ever had that tail walking about 3 or 4 times. The S4 is more sensitive to adjustments of mast foot position than the S3. I only ever move the mast foot on the S3 by 1cm (for 6.5m/7.5m or flat/choppy water or in light to strong winds), whereas the S4 by 2cm (just with 8.5m).
Footstrap positions. When I had by Falcon 125 I sailed it with 7.6m & 9m. With the 7.6m when slalom racing, I found I needed to put the footstraps at 1 hole from the front (out of 4). Too far back and it was too lively for me. It want so good for the 9m, but we didnt race in 9m winds. After I stopped racing and just used it with a 8.5m, I moved the straps 1 hole back to get it flying off the fin more. Maybe try the straps forward a hole. It depends on how often you have the problem.
Its also technique. Sailing well powered in swell when you sometimes jump is a lot harder than flat water. Wimp out and sheet out a bit when it would be better going flat out doesn't help. By that stage I'd be changing down whereas better sailors carry on.