Withdrawal delay.
the video in the post shows that rendering occurs at an interval of about 1 second. No data is received in realdash. Only GPS is included. The same thing happens on the other device.
if you connect OBD, nothing changes. The tachometer data is polled in the same way with an interval of about 1 second.
Sorry for my English

I think what you are experiencing is a GPS drift. That is quite common phenomenon with GPS that your location drifts for a few meters and produces small speed values even when you are not moving at all.

This is not GPS drift.
The same thing happens with any sensor. I wrote above that this happens with the tachometer when connected to the car.
Moreover, this happens on two different devices,
RockChip PX5 4Gb RAM - car
Smartphone Xiaomi Mi5S Plus 4Gb RAM

This has always happened since the first installation of Realdash (almost a year),
There just wasn’t time to get serious

Any readings change at 1 second intervals.
It’s just that it’s not noticeable on slow sensors.

more descriptive video.
The interval is very noticeable.
When there are little or no changes, the vehicle moves at a constant speed.

GPS speed probably always updates at 1hz unless you have external high performance GPS unit. So still I think that is just a nature of the GPS. You can add smoothing to that gauge to appear less jerky.

If all other inputs (which I have not seen on video) update slowly it must be that your vehicle is just not sending the data any faster. You can see the data rate from input 'Data update rate (values/s).