I don't know what to do for the best

maybe I'm not letting ACF50 do its job properly. but surly reapplying after each wash should be ok? or is it just the bike that hates the rain salt and ice
I suppose you have to narrow it down, it can't be many things;
If your bike is more prone to rust than others, either; 1. Your bike is not getting protected properly, or 2.It is being subjected to worse conditions than others.
On point 1 - if you're washing it well and letting it dry, questions would be;
- Are you putting enough rust protection on?
- Are you using something that is lessening the effect of the ACF50, or causing corrosion itself?
Possible candidates - aggressive jetwashing, using washing up liquid (which has salt, I was told this on this board) instead of car shampoo or similar. Not really letting it dry properly, and then leaving it in a plece where the moisture becomes trapped (under a tarp / in a damp garage?).
When you're wiping the ACF50 on, are you using enough, and does the cloth have any contaminants on it? ACF50 is usually sprayed or brushed on, then cleaned up with a cloth. It's cheap stuff, don't skimp on it.
Is your riding high speed, and in spray or similar? Following a truck on a rainy motorway is probably about the same as jetwashing the bike.
There are probably a million other possibilities, but it will boil down to one of the two possible causes.
There's no reason not to clean the bike as often as you like, and in theory the ACF50 should survive a certain amount of water being sploshed on it, but you certainly have to make sure it's on the bike.