tl;dr: If you don’t look at that jumpy number and just listen, it is probably sync’d tight.
The BPM display on the Digitakt isn’t very smoothed. All MIDI sync followers are internally taking a jittery signal and smoothing it out. There is a trade-off in smoothness with how fast it can respond to actual tempo changes.
Practically speaking, by ear alone you’d want the follower to be quicker and more responsive. But the visual display looks jumpy if you show that directly. So implementations often smooth the display even more. On the Digitakt they seem to have opted to just showing you the internal state.