sounds like the shortcut is not active at all if the space key in general still works. Can you assign actions to space key without condition?
Is it a global shortcut or an app specific one?
Yes, it is working fine here with 3.870
Could you copy the json for the shortcut here?
[
{
"BTTTriggerType" : 0,
"BTTTriggerClass" : "BTTTriggerTypeKeyboardShortcut",
"BTTPredefinedActionType" : -1,
"BTTPredefinedActionName" : "Keine Aktion",
"BTTLayoutIndependentActionChar" : "a",
"BTTAutoAdaptActionToKeyboardLayout" : true,
"BTTShortcutToSend" : "0",
"BTTAdditionalConfiguration" : "0",
"BTTEnabled2" : 1,
"BTTKeyboardShortcutKeyboardType" : 3809,
"BTTRepeatDelay" : 0,
"BTTUUID" : "D9498730-9042-432F-93BD-441FA0E7D1A2",
"BTTTriggerOnDown" : 1,
"BTTNotesInsteadOfDescription" : 0,
"BTTLayoutIndependentChar" : "SPACE",
"BTTEnabled" : 1,
"BTTModifierMode" : 0,
"BTTShortcutKeyCode" : 49,
"BTTShortcutModifierKeys" : 0,
"BTTOrder" : 1,
"BTTDisplayOrder" : 0,
"BTTAutoAdaptToKeyboardLayout" : 0
}
]
Looks good to me and seems to work as expected here. Not sure what could cause it to not be registered, maybe some other app catches the space key before BTT can?
I don't know what app that could be, keyboard maestro? I closed it, but the result remains the same. Anyway, thanks for your time, I do it with key sequences, that works fine. I just asked you because it would be better not to have undo. But it is good this way 
I found the problem and fixed it. It works now. But you are right.
True. That's why I don't use it.
oh what caused the issue?
Honestly? Here? It has something to do with "prevent recursive triggers" and repeating. Very technical 