This article will be of interest to you if you have an FAMC LF+ MIDI controller. I'm writing this to share something that only seems obvious now that I've figured it out. I thought I'd share this to save others a bit of head-scratching.
Bear in mind that this is neither a complaint nor a request for enhancement. When you think about what I'm about to tell you, it's pretty obvious that the LF+ must work this way.
Here's the executive summary. If you have an IA function that's extremely sensitive w.r.t. timing, do not put a 2nd function on the same button.
For me, this became obvious only on an IA used to control my phrase looper. Timing is everything; you want the looper to begin recording exactly when you tap the button, and close the loop exactly when you tap whatever LF+ button triggers that function on the looper.
If you assign a 2nd function to one of the buttons used for a timing-critical control, the function is not invoked when your foot hits the button.
Why not? That's because the LF+ can't know your intent, but rather has to wait to see whether you're trying to access the 2nd function. I know this applies if your 2nd function is accessed via a long press; I suspect it must also be true if you use a double-tap to access the 2nd function.
Think about it. Your foot hits the button. What's the intent? Do you want to access the 1st function or the 2nd function? That's not known until you either hold the button long enough to access the 2nd function (or until you complete a double-tap). The 1st-function command can not be sent until you take your foot off the button prior to the long-press timing threshold (or, I suspect, until the double-tap detection time has expired without a double-tap).
So: if you have a timing-critical command, put it on a button that doesn't have a 2nd function assignment.