A2A latest update (May 2020) was for FSX and P3Dv1-3. Not sure if the FSX-P3V1-3 updater even works to update the FSX-SE version but don't think so.
You might have to post at A2A. I'm sure if you make contact with Scott or Lewis there they will assist and advise. But the latest A2A update for the J3 (v1.1) doesn't mention fixes to get off the water with floats and that's the only fix since 2009 when the J3 was released.
Now that accusim J3 only had a 65 hp engine.. (J3 Accusim) so you need to have the engine warmed up (If you haven't warmed it up but have pushed over it's limit then you have probably have damaged that engine.
(So might have to go into the maintenance hanger and check the engine (and fix it/overhaul it).
J3 Manual pdf-Direct LINK>>
https://www.a2asimulations.com/Manuals/P3D/Accusim_Cub_Manual_P3D.pdf(Refer to page 10, 11 and 12)
Also that float version - you need a big lake to get enough speed to get off the water. but have to use power, no flaps (until up to take off speed), push the stick down so the nose is down on the water for the least amount of drag possible on the pontoons then when up to speed a slight sharp up to break free of the water surface then slow climb to continue gaining airspeed. There is a trick to it. But check that engine first!.
The Accu-Sim Update 11/05/2020 (May 11 2020) Download - FSX and P3D v1-v3
>LINK:
https://a2asimulations.com/forum/viewtopic.php?f=23&t=57819" This one A2A update detects and updates our fleet of Accu-Sim aircraft for FSX and Prepar3D v1-3 (with the exception of the latest release, the Bonanza V35B). For Prepar3D v4 and the Bonanza, new installers which will automatically detect any updates are available. Please see this post for more details.
Hope something in this post helps get your J3 off the water!
Norm