They're not hard-realtime, so they definitely can miss a few samples. You can workaround that by reconfiguring an external device rather than generating the samples locally, but that's not what Ableton or FL do.

Win and Mac have soft-realtime scheduling and the mentioned software does what it can without guarantees https://help.ableton.com/hc/en-us/articles/209072289-How-to-... I've been to a live gig before where the performance was paused a few times because artist's mac was misbehaving.